In (NaOH)0.5NbSe2, the electric decoupling is manifested by an ideal 1D insulating state along the interlayer direction. Vibration decoupling is demonstrated through the absence of interlayer models in the Raman spectrum, dominant local modes in heat capacity, low interlayer coupling energy and out-of-plane thermal conductivity (0.28 W/mK at RT) that are reduced to a few percent of NbSe2’s. Consequently, a drastic enhancement of CDW transition temperature (>110 K) and Pauling-breaking 2D superconductivity is observed, suggesting that the bulk crystal behaves similarly to an exfoliated NbSe2 monolayer. Our findings provide a route to achieve intrinsic 2D properties on a large-scale without exfoliation.Interlayer decoupling plays an essential role in realizing unprecedented properties in atomically thin materials, but it remains relatively unexplored in the bulk. It is unclear how to realize a large crystal that behaves as its monolayer counterpart by artificial manipulation. Here, we construct a superlattice consisting of alternating layers of NbSe Interlayer decoupling plays an essential role in realizing unprecedented properties. Here, authors construct a superlattice consisting of alternating layers of NbSe2 and highly porous hydroxide, realizing interlayer decoupling and thus realizing exotic monolayer behaviors in bulk materials. Compared to the bulk, isolated monolayers show a rich variety of distinct properties owing to their interlayer decoupling, both electrically and vibrationally. For instance, graphene displays exceptional electronic transport properties and stiffness6. Monolayer NbSe2 host exotic electronic states, including drastically enhanced charge-density wave (CDW) order and Ising superconductivity8. Black phosphorus9 and MoS22 undergo indirect to direct band gap transitions as their thickness is reduced to the monolayer limit. These examples demonstrate that interlayer decoupling significantly impacts mechanical, electrical, and optical properties. However, when considering aspects such as fabrication, chemical and environmental stability, and sample quantity, bulk materials continue to outperform their monolayer counterparts. Therefore, it is highly desired to find a route to realize interlayer decoupling in large crystals, so that intrinsic 2D properties can be realized in bulk materials.Since the discovery of graphene14. However, this ability is notably absent in bulk materials. For an exfoliated monolayer, the vibrational and electrical connections to the bulk are interrupted by the surrounding vacuum or air  can be even lower than that of air22. Inspired by the extraordinarily hollow and disordered structure of aerogels, we construct some hydroxide layers with extremely high porosity, i.e., up to 95% of the volume in some hydroxide layers remains vacant. These fluffy aerogel-like layers (~2 nm) facilitate the lattice matching with a variety of transition metal dichalcogenides (TMDs) and give rise to a new family of bulk superlattices 0.5NbSe2. Systematic investigations suggest that the thick and porous NaOH layers act as superinsulators and detach the NbSe2 monolayers spatially, electrically and vibrationally, as confirmed by X-ray diffraction, Raman spectrum, heat capacity, heat transport measurements, orientation and temperature-dependent resistivity, and density functional theory (DFT) calculations. Moreover, the fitting of angle-dependent magnetic resistance and magnetic torque data reveal that the exotic superconductivity and CDW states in bulk (NaOH)0.5NbSe2 are consistent with those found in NbSe2 monolayer, suggesting this decoupled bulk crystal act just like an exfoliated NbSe2 monolayer. The concept of introducing aerogel-like layers to decouple the bulk materials can be easily extended to other TMDs materials  up to 0.6 cm in size were synthesized under hydrothermal conditions by using MX2 single crystals as the precursor (detailed in methods). In the case of (NaOH)0.5NbSe2, the X-ray diffraction data in Fig. 2 precursors are completely replaced by a new set of ones that systematically shift to lower angles, suggesting the incorporation of new block layers into the NbSe2 layered structure. Figure 2. XPS analysis was carried out on a freshly cleaved single crystal to probe the species and the oxidation states of the elements in NbSe2 and (NaOH)0.5NbSe2, with the corresponding Nb3d, Se3d, Na1s, and OH- spectra presented in Fig. 3d and Se3d spectra of pristine and the intercalated NbSe2 have identical binding energies, indicating the oxidization state of NbSe2 is unaltered upon reaction, and there is no evidence of charge transfer between the block layer and the NbSe2 matrix. Meanwhile, a sharp peak at 1070 eV was ascribed to the Na+25, and the peak at 532.4 eV was assigned to OH-, confirming the NaOH molecules as the intercalants. The shoulder peak at 529.1 eV corresponded to a trace amount of adsorbed water molecules, rather than hydrated water in the structure26. From this, the chemical formula of the intercalated samples can be best described as (NaOH)0.5NbSe2.As shown in Figs. 0.5NbSe2, single-crystal X-ray diffraction (SXRD) analysis was implemented on a small specimen (132 × 74 × 17 μm3). The SXRD diffraction data can be indexed by a trigonal unit cell (space group P-3m1), with lattice parameters a = 3.4554 Å, c = 48.9648 Å  sites, which form ~2 nm thick NaOH trilayers in between the NbSe2 monolayers. It is worth noting that the resolved electron density of the two outmost NaOH layers is much lower , and two times that of most known intercalated NbX2  compounds27, confirming the NbSe2 monolayers are well spatially detached. More strikingly, structure refinement suggests only 5 % of the sites in the two outmost layers are randomly occupied by NaOH molecules, consistent with the results of charge density analysis . The occupancy of the central NaOH layer reaches 40 %, which is necessary to brace up the structure framework.To determine the crystal structures of (NaOH)8 Å Fig. . Form th8 Å Fig. , the NaOwer Fig. , suggestOH Table . As showsis Fig. . The den2 single crystals used here are all metallic28, and the reported electrical anisotropy ρab(T) and ρc(T) are in-plane and out-plane resistivities, respectively)29. By inserting ~ 2 nm thick AOH layers in between the MX2 layers, giant electronic anisotropy appeared in all (AOH)xMX2 materials, which behave as either band insulators or metals, depending on the measured crystal axis  and ρc(T) data of NbSe2 and (NaOH)0.5NbSe2 measured between 3 K and 300 K. Along both a- and c- directions, the NbSe2 single crystal show metallic behavior, where the measured β was negligibly small - less than 2.5 at 300 K. At 7 K, a superconducting transition is observed  at low temperature can be well fitted by a semiconducting thermal activation model  is very small, generally in the order of ~10, while their β can be further increased to ~103−104 by the intercalation of molecules or inorganic layers31. The recent incorporation of 1 nm thick, stoichiometric Ba3NbS5 layers in quasi-2D superlattice Ba6Nb11S2818 increased the β values to around 103, which is three orders of magnitudes smaller than the maximum value realized in (NaOH)0.5NbSe2. The huge resistance anisotropy and especially the insulating behavior of ρc(T) suggest that the thick hydrate layers have effectively eliminated the interlayer electronic couplings between NbSe2 monolayers.Electrical anisotropy is generally small in metallic crystals. However, in the case of a fully decoupled metal, an insulating behavior is expected along the interlayer direction, whereas metallic behavior should be retained for in-plane directions. The MXis Figs.  and S4a.ved Fig. . After idel Fig. . Interes0.5NbSe2, bulk NbSe2 and monolayer NbSe2. For (NaOH)0.5NbSe2, all bands crossing the Fermi level are contributed by the spatially detached NbSe2 layers, resulting in nearly identical band structures and fermi surfaces of (NaOH)0.5NbSe2 and monolayer NbSe2. In bulk NbSe2, the degeneracy of the Nb 3d band that crosses the Fermi level is broken by the interlayer coupling with bonding/antibonding configurations of Se pz orbitals, which gives rise to two split bands in the Γ-M-K-Γ plane and two concentric cylindrical Fermi surface. In the monolayer form, the interlayer coupling is absent, both bands shifting of Se pz orbitals across the Fermi level and the band splitting of Nb 4d orbitals are avoided, leaving only one Nb band across the Fermi level. In (NaOH)0.5NbSe2, the Se pz conducting bands are found to sink below the Fermi energy, and the band degeneracy of Nb 4d states is almost perfectly preserved, leading to a monolayer-like band structure without interlayer couplings32. Moreover, in bulk NbSe2, the antibonding between interlayer Se pz orbitals lift the Se 3p band across the Fermi level, creating a small Fermi surface with strong kz dispersion. In (NaOH)0.5NbSe2, the band structure exhibits only the dispersionless flat bands along the Γ–A direction. Therefore, like monolayer NbSe2, the fermi surfaces of (NaOH)0.5NbSe2 are derived from a single (or degenerate) Nb 4d band that is dispersionless along the kz direction, confirming the elimination of interlayer electronic couplings.Figure 2 layers in (NaOH)0.5NbSe2 separated by sparse NaOH layers are also decoupled vibrationally. Figure 2, monolayer NbSe27 and (NaOH)0.5NbSe2, respectively. The NbSe2 intra-layer vibration models, including E2g mode at ~250 cm−1, A1g mode at ~220 cm−1, and the soft mode at the range from 150 to 200 cm−1, were observed in all three samples. However, the most known interlayer vibration model in bulk and few-layer NbSe2, which manifest itself as a strong low-frequency vibrational band (20–30 cm–1), is absent in monolayer NbSe2 and (NaOH)0.5NbSe2. The absence of low-frequency shearing modes in the Raman spectrum of NbSe2 is only found in its monolayer form, implying that in (NaOH)0.5NbSe2, interlayer vibration couplings between NbSe2 monolayers are effectively eliminated by introducing thick aerogel-like NaOH layers.Besides electronic decoupling, we demonstrate that the numerous NbSe0.5NbSe2 can be treated as independent harmonic oscillators (or Einstein oscillators), similar to clathrates and filled-skutterudites, whereas the remaining lattice can be treated within the Debye model. Figure Cp of (NaOH)0.5NbSe2 in the range of 2–300 K, with a fitting curve using a combined Debye–Einstein mode . A minimum of two Einstein modes are required to adequately model the temperature dependence of Cp, whose characteristic temperatures were determined to be 0.5NbSe2 is localized. Considering the chemical bonds within the NbSe2 layers are intact and strong, we believe the localized phonon is confined by the weak interlayer bonding between the sparse NaOH layers and NbSe2 layers, with the absence of up to 95% of the chemical bonds.The vibrationally decoupled substructures in (NaOH)0.5NbSe2 along the interlayer direction, the thermal conductivity of a (NaOH)0.5NbSe2 single crystal is measured using the beam-offset time domain thermos-reflectance (TDTR) method33. In Fig. Vin) to the out-of-phase voltage (Vout) of the measured TDTR signals with the ratio calculated from a thermal model. As shown in Fig. ⊥ is determined to be merely 0.28 W m−1 K−1 within experimental uncertainties, which is drastically reduced to 7% of bulk NbSe2 0.5NbSe2 can be attributed to the ultralow interlayer coupling strength of (NaOH)0.5NbSe2, which leads to the much-reduced group velocity of lattice vibrations along the out-of-plane direction. In order to evaluate the anisotropy of thermal conductivity, we measured the in-plane thermal conductivity κ∥ of (NaOH)0.5NbSe2 single crystal using a steady-state heat flow setup 0.5NbSe2 was measured in the temperature range of 150–350 K, and the results are presented in Fig. κ∥ is 98.1 W/mK, suggesting the thermal conductivity anisotropy 38, and exceeds that of pyrolytic graphite (PG)—one of the most anisotropic bulk thermal conductors (Δ ≈ 340)39.To experimentally verify the vibrational decoupling in (NaOH)Se2 Fig. . The thrtup Fig. . The κ∥ 2 atomic layers, which gives the theoretical interlayer coupling energy E. As shown in Fig. 2 monolayers are indeed weakly coupled to NaOH layers in (NaOH)0.5NbSe2. The interlayer coupling energy E only reached 2.5 meV/ Å2, around 9 % of that of bulk NbSe2 (25 meV/Å2). Such a small E is even comparable to the low coupling energy that found in exfoliated monolayers deposited on different substrates40. Naturally, the low occupancy factor in aerogel-like NaOH layers (Occ = 0.05) is expected to reduce the strength of the vdWs interactions. To clarify how partial occupancy affects the interlayer coupling energy, we performed DFT calculations based on structure models with a range of Occ between 0.05 and 1.0. As shown in Fig. 2 at Occ = 1.0, a value similar to that of pristine NbSe2. The findings suggest the ultralow density (or Occ) in aerogel-like NaOH layers plays a crucial role in reducing the interlayer coupling in (NaOH)0.5NbSe2. Figure ⊥, both of which should approach 0 when the material is perfectly decoupled. It shows that (NaOH)0.5NbSe2 exhibits both very low interlayer coupling energy and κ⊥, and more than 90% of them in pristine NbSe2 is removed by incorporating the highly porous NaOH layers, pushing (NaOH)0.5NbSe2 toward the best bulk material in terms of interlayer decoupling.To get an insight into the observed interlayer decoupling at the atomic level, we have calculated the potential energy curves by elongating the interlayer distance between NbSe2, the CDW transition is generally below 33 K7. In monolayer NbSe2, the electron-phonon interactions are significantly enhanced in the 2D limit, leading to a remarkable enhancement of the charge density wave (CDW) phenomenon  under TCDW. In Figs. 0.5NbSe2. From 300 K to 140 K, the spectra are relatively clean and agree well with monolayer NbSe2 above its TCDW. The prominent features below 300 cm−1 include an E2g mode around 250 cm−1, an A1g mode around 220 cm−1, and a soft model around 170 cm−1, with the absence of the interlayer shear model in bulk NbSe2. Below 140 K, two new modes appear in the Raman spectra. The first new mode emerged around 190 cm−1, and the second feature is a broad amplitude mode that appeared around 75 cm−1, both of which were observed in the CDW-state of bulk NbSe2 and monolayer NbSe2 below TCDW and were attributed to the collective excitation of the CDW fluctuations. As shown in Fig. 0.5NbSe2, the CDW-related vibrational modes appeared much higher than 33 K, indicating an enhanced TCDW. Figure ICDW of the CDW-related model at 190 cm−1. The TCDW of (NaOH)0.5NbSe2 should be below the temperature where ICDW dropped to zero. The temperature dependence of ICDW in bulk and monolayer NbSe2 taken from pieces of literature are also presented in Fig. 7. As for (NaOH)0.5NbSe2, the intensity of the CDW-related Raman peak vanishes between 110 and 140 K, and the significantly enhanced CDW order is in line with the findings in monolayer NbSe2. Moreover, the amplitude mode and folding mode corresponding to CDW in (NaOH)0.5NbSe2 are much stronger than in monolayer NbSe27. Since the intensity of the Raman signal is proportional to the number of layers, the enhancement here is likely to be caused by the superposition of many monolayer signals.The CDW transition usually involves lattice distortion in which the electron-phonon coupling plays an important role. In bulk NbSe0.5NbSe2. Torque magnetometry measures the torque M experienced in a uniform magnetic field H (μ0 is the permeability of vacuum), where the V. This technique is particularly useful for studying CDW systems because the CDW order often leads to changes in the magnetic susceptibility. In the case of H-NbSe2, the CDW order is known to arise within the Nb atomic layer. Both H-NbSe2 and (NaOH)0.5NbSe2 feature Nb atomic layers with a D3h symmetry, which can be equally described in an orthogonal lattice using new crystallographic axes, namely ao and bo 0.5NbSe2 single crystals using a setup depicted in Fig. 2 maintained a two-fold Sine function (with a period of π) throughout the CDW transition. This observation is consistent with the retention of D3h symmetry in the 3 × 3 CDW phase of NbSe2. Below the CDW transition temperature, we observed a significant increase in the amplitude of τ2φ, indicating enhanced magnetic anisotropy between different susceptibility tensors in the CDW phase  form in both the normal state and below the TCDW (as determined by Raman scattering), strongly suggesting that the CDW phase in (NaOH)0.5NbSe2 also retained the D3h symmetry as in the 3×3 CDW phase of H-NbSe2. Meanwhile, the drastic increase of magnetic torque strength, signifying the onset of CDW ordering, occurred at much higher temperatures in (NaOH)0.5NbSe2 (>120 K), in consistency with the Raman scattering results.With the advantages of bulk crystals, we can directly use torque magnetometry to reveal more details about the CDW in (NaOH) bo Fig. . In the ase Fig. . For 0.5NbSe2 relative to bulk H-NbSe2 is consistent with NbSe2 monolayer (Tc = 1.5 K)24. Noticeably, the ρab(T) for (NaOH)0.5NbSe2 for 1.5 K < T < 1.8 K is well described by the Halperin-Nelson model41: At last, we turn to the superconducting state of (NaOH)Tc, the exotic Pauli-breaking Ising superconductivity appeared in monolayer NbSe2, few-layer NbSe2 and Ba6Nb11S28 vdWs superlattice has attracted intensive attentions8. For a superconductor, applying an external magnetic field can suppress its superconductivity either via. the Zeeman effect or through in-plane orbital effects. The Zeeman effect, in particular, imposes an upper bound on the critical magnetic field, known as the Pauli (or Clogston–Chandrasekhar) limit (42. The Pauli violation ratio (PVR), defined as μ0Hc‖(0)/μ0HP, is generally smaller than 1.0 for conventional superconductors, including bulk NbSe2. In monolayer NbSe2, Pauli-limit violation Ising-superconductivity can be achieved in the presence of finite-momentum pairing or strong spin–orbit coupling (SOC)8. In bulk superlattice Ba6Nb11S28 and few-layer NbSe2, some exotic Pauli-breaking Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state and orbital-FFLO state 2D superconductivity are also reported recently43. In (NaOH)0.5NbSe2, we show that its 2D superconducting behavior is more like the Ising-superconductivity appeared in monolayer NbSe2. In Fig. μ0Hc2-T/Tc diagram for (NaOH)0.5NbSe2 clearly shows that the Pauli violation ratio (0)/2 and well above the PVR values in Ba6Nb11S28 and few-layer NbSe243. In terms of anisotropy in both the normal state resistivity (β) and superconductivity (γ), the values in (NaOH)0.5NbSe2  are much higher than that in the ‘layer-in-cake’ 2D superconductors Ba6Nb11S28  and Ba6Nb11Se28 31. Moreover, considering the absence of sharp shapes of 2 and Ba6Nb11S28, and the high value of PVR that also exceeds the limit of Rashba-type SOC, it is reasonable to assign the Pauli-breaking superconductivity in (NaOH)0.5NbSe2 to the effect of Ising paring without FFLO, a mechanism that well acknowledged in monolayer NbSe2. Above all, the drastic enhancement of CDW above 110 K as well as the occurrence of exotic Pauli-breaking 2D superconductivity below 1.5 K, consistently suggests that the (NaOH)0.5NbSe2 bulk crystal behave just like a decoupled NbSe2 monolayer.Despite the decrease in 2 , resulting in large single crystals consisting of ~2 nm thick, porous hydrate layers and MX2 monolayers. The elimination of interlayer electron couplings turns the metallic parent materials into ‘insulators’ along the interlayer direction, whereas along other crystallographic axes the metallic state remains. The vanished interlayer electron couplings are also supported by the ideal 2D electronic band structure and fermi surfaces. Fascinatingly, the rarely occupied (5%) hydrate layers also cut off the interlayer vibrational coupling in bulk (NaOH)0.5NbSe2, leading to an extremely low interlayer coupling energy of 2.5 meV/Å2 and interlayer thermal conductivity of 0.28 W m−1 K−1. The disappearance of the interlayer shearing vibrational model, the appearance of two CDW-related models well above 110 K and the exotic Pauli-breaking 2D superconductivity below 1.5 K are nearly identical to the behaviors found in NbSe2 monolayers. Our findings suggest the insertion of highly porous (aerogel-like) block layers can effectively decouple the monolayers in 3D crystal lattices, so that intrinsic 2D properties can be realized in conventional bulk materials.In conclusion, we have developed a method to fabricate aerogel-like superlattices by incorporating hydrate molecules AOH  into MX2  crystals were grown from M powder of 99.95 % purity and X pellets of 99.999 % purity by iodine 99.8 % vapor transport in a gradient of 730–700 °C in a sealed quartz tube for 15 days. Then, 0.3–0.6 g of thiourea  and 1–2 g AOH   were dissolved in 10 ml of ammonium sulfide aqueous solution (14 % in water) in a Teflon-lined stainless-steel autoclave (volume 25 mL). Then, several pieces of MX2 crystals were added to the solution. Finally, the autoclave was sealed and heated up to 100–130 °C for 130 h. Upon recovery, large (NaOH)0.5NbSe2 single crystals with a different silver metallic luster were obtained by leaching and clearing.For the first step, MXPowder X-ray diffraction (PXRD) patterns were collected at room temperature on a Rigaku smart Lab X-ray diffractometer operated at 40 kV voltage and 40 mA current using Cu Ka radiation (λ = 1.5406 Å). The 2θ range was 10–80°with a step size of 0.01. Indexing and Rietveld refinement were performed using the DICVOL91, Fullprof, and MDI Jade programs. Single crystal X-ray diffraction (SCXRD) patterns at 295 K were collected using a Bruker D8 VENTURE PHOTO II diffractometer with multilayer mirror monochromatized Mo Kα (λ = 0.71073 Å) radiation. Unit cell refinement and data merging were performed using the SAINT program, and an absorption correction was applied using multi-Scans scanning. Structural solutions with the P -3 m 1 space groups were obtained by intrinsic phasing methods using the program APEX3, and the final refinement was completed with the Jana 2020 suite of programs. The electron density maps of the two samples were first constructed by the charge flipping method implemented in the Jana2020 software. Scanning electron microscopy (SEM) images were taken on a Phenom pro XL microscope equipped with an electron microprobe analyzer for the semiquantitative elemental analysis in the energy-dispersive X-ray spectroscopy (EDS) mode.The torque measurements used commercial components provided by Quantum Design Company (TRO Torque Magnetometer). As illustrated in the inset of Fig. 44. We adopted the generalized gradient approximation (GGA) in the form of Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation potential45. The projector augmented-wave (PAW) pseudopotentials were used with a plane wave energy of 500 eV; 4s24p4 for Se, 4p64d45s1 for Nb, 2p63s1 for Na, 2p42s2 for O and 1s1 for H electron configuration were treated as valence electrons. A Monkhorst-Pack46 Brillouin zone sampling grid with a resolution of 0.02 × 2πÅ−1 in the self-consistent calculation and 0.01 × 2πÅ−1 for Fermi surface calculation were applied. The position of H in (NaOH)0.5NbSe2 was manually added and the position of H and O were relaxed until all the forces on them were less than 0.1 eV/Å. The lattice constants were derived from the experimental results. The van der Waals interaction was considered using the DFT-D3 method of Grimme48. The total energy of the system as a function of interlayer separation is calculated by using GGA-PBE (Perdew–Burke–Ernzerhof) functional, as implemented in the CASTEP code. The kinetic energy cutoff for the plane-wave basis set was 410 eV. In the self-consistent potential and total energy calculations of NbSe2 layers, a set of (8 × 8 × 1) k-point samplings was used for Brillouin zone integration. The convergence criterion of self-consistent calculations for ionic relaxations was 10-4 eV between two consecutive steps. By using the conjugate gradient method, all atomic positions and unit cells were optimized until the atomic forces were 0.05 eV/Å.were performed within the Vienna ab initio simulation packagein and the out-of-phase Vout signals from the rf lock-in amplifier to calculations using a thermal model. The in-plane thermal conductivity on a (NaOH)0.5NbSe2 single crystal was measured using a steady-state four-contact method on a custom-built small sample experiment mounted on a furnace which integrates a calibrated heat-pipe in series with the sample.The out-of-plane thermal conductivity was measured using time-domain thermoreflectance (34). The pump and probe beam optical beams are focused on the surface of the samples using a microscope objective lens. The thermal conductivity is determined by comparing the time dependence of the ratio of the in-phase Vab(T) of NbSe2 and (NaOH)0.5NbSe2 samples were measured in a standard four-probe configuration with the applied current less than 2 mA. The out-of-plane resistivity ρc(T) of NbSe2 and (NaOH)0.5NbSe2 samples were measured using the Montgomery methods. Measurements in magnetic fields up to 18 T were conducted.Resistivity measurements were carried out using a SQUID PPMS-9 system  and a home-made low temperature and high magnetic field transport measurement system . Temperature dependence of the in-plane resistivity ρSupplementary InformationPeer Review File


Objective: To establish the areas of research focus in the application of VR in rehabilitation medicine, analyze its themes and trends, and offer a reference for future related research in this field. Methods: This paper provides an in-depth analysis of the development process, areas of research focus, and research trends in the field of the application of VR in rehabilitation medicine, using the Web of Science core dataset as the source and using a bibliometric analysis with CiteSpace. Results: The application of VR in rehabilitation medicine was composed of three stages, and the research topics were reviewed from five perspectives: neurological rehabilitation, psychological treatment, pain distraction, cardiopulmonary rehabilitation, and visual–spatial disorder. Limitations: The research data were sourced from the Web of Science core dataset only, and the data-sample size was not comprehensive. Conclusions: Overcoming VR-technology-induced vertigo, mental disorders from the overuse of VR, individualized treatments, and integration with traditional therapy are all challenges in the application of VR in rehabilitation medicine that require research. In addition, developing VR products with better experiences, constructing standardized guidelines, and conducting more high-quality clinical studies are all future research topics related to the application of VR in rehabilitation medicine. Virtual reality (VR) is a multidisciplinary technology that generates a virtual digital world through computer simulations and provides complex, realistic, and immediate feedback similar to reality using software programs and hardware devices  to give users an immersive feeling and experience . In receRehabilitation medicine aims to improve the quality of life of sick, injured, and disabled people and their eventual integration into society. Because VR has the characteristics of virtual tasks, interesting scenarios, and high levels of user participation, VR technology can be a realistic and convenient tool for all rehabilitation subjects to adapt to the real world in advance, and it can achieve excellent therapeutic effects in rehabilitation. In recent years, VR technology, as a frontier technology in rehabilitation medicine, has shown great advantages and is increasingly used in multiple fields, such as neurological rehabilitation, pediatric rehabilitation, orthopedic rehabilitation, etc. For example, the use of a commercial wearable head-mounted display (HMD) and selected VR motion games for Parkinson’s disease to maintain physical and functional abilities has shown good disease-management effects ; a VR-baAfter reviewing relevant studies, this research found that although there are numerous studies on this topic, most of them focus on the feasibility and effectiveness of VR technology for rehabilitation training for certain types of patients. To the best of our knowledge, there has been no systematic research on the areas of research focus and research trends in the application of VR in rehabilitation medicine. Therefore, this paper systematically reviews the literature on the application of VR in rehabilitation medicine and summarizes and analyzes the areas of research focus, thematic evolution, and development trends in this field through bibliometric methods, aiming to deepen the understanding of the application of VR in rehabilitation medicine and provide a reference and theoretical basis for subsequent related research.This article uses CiteSpace as a bibliometric analysis tool. Currently, Citespace software allows the individual analysis of research imported from various databases, such as PubMed, Web of Science, Scopus, etc. However, it does not currently offer the ability to merge and analyze research from multiple databases together. Among the various databases, the Web of Science Core Collection is a comprehensive academic database that covers multiple disciplines. The research indexed in the Web of Science Core Collection holds high academic value and reliability. Hence, it was chosen as the data source for this study.The search strategy was as follows: TOPIC:  AND . The item type was “article”, and the time range was up to 2022. In total, 3448 articles were obtained. The retrieval date was 16 January 2023.CiteSpace is a literature information visualization tool developed by Prof. Chaomei Chen’s team at Drexel University, USA. This study first used Excel 2019 to conduct a basic statistical analysis of the number of annual publications; then, national  collaboration network analysis of the literature was conducted through CiteSpace, as well as keyword co-occurrence network and co-word timeline network analysis to explore the development history, areas of research focus and frontier topics of VR in rehabilitation medicine research .The interannual variation in the number of publications can visually reflect the distribution of the literature on the application of VR in rehabilitation medicine. By mapping national  collaborative research, it is possible to visually observe the sources of academic productivity of research on the application of VR in rehabilitation medicine and to understand the core strengths and mutual collaborative relationships in this research field. In this study, CiteSpace was used to generate a national collaborative network, as shown in By analyzing the keyword co-word network of the literature, the relevance of keywords to the research focus in specific academic fields can be explored. With the emergence of VR products, researchers began to discuss the existing and potential applications of VR technology in rehabilitation, such as the prospect of the application of VR in neurological rehabilitation  and the Furthermore, VR-based therapies have commenced exploration of their application in a variety of diseases, such as the visual and auditory stimulation generated by VR technology for communication with and the education of autistic children . AdditioIn 2010, Microsoft launched the motion-tracking sensor “Kinect”, which has made significant advances in both graphics processing and motion capture technology, further promoting research on the application of VR in rehabilitation medicine. Designing rehabilitation games through Microsoft Kinect for sports rehabilitation exercises for Parkinson’s disease (PD) patients could effectively motivate their exercise interest . HemipleAnother representative product is Oculus Rift, an immersive virtual environment using a very inexpensive wide field of view, which was launched by Oculus in 2013. Oculus Rift Virtual Reality (VR) goggles could elicit a strong illusion of presence and reduce pain through VR, which can be applied to daily burn wound care and physical therapy, enabling more patients (possibly even at home) to conveniently use VR for pain control . AnalysiIn 2014, Google released its VR product Cardboard. Because of its low price and positive experience, its application in rehabilitation has also developed rapidly, which was beneficial for the rehabilitation therapy of patients with mechanical strabismus and/or amblyopia who have lost eye movements . An immeAt this stage, new VR products are constantly being launched, represented by Meta Quest 1 released in 2019 (Meta Quest 2 released in 2021), more commonly known as Oculus Quest. Meta Quest is a standalone device with high degrees of freedom and hand-tracking capabilities. Meta Quest offers various applications in the field of rehabilitation, such as shoulder rehabilitation , knee osAdditionally, as VR technology matures, a growing number of manufacturers have developed personalized VR devices for different patients to build targeted training scenarios. The serious game REHAB FUN VR environment developed with the Unity engine helped children with cerebral palsy improve their motor and cognitive abilities . A novelFrom the analyses of keyword clustering and theme evolution, the research on the application of VR in rehabilitation medicine involves gait balance, stroke, Parkinson’s disease, cerebral palsy, neurorehabilitation, cognitive rehabilitation, brain injury, pulmonary rehabilitation, depression, etc. Meanwhile, 3448 papers were selected for abstract reading by the co-authors of this study and classified by research topic based on abstracts. Eventually, based on high-frequency keyword statistics, clustering, and theme evolution path, and combined with the content of the classical literature by co-authors, the research themes are summarized into the following five dimensions for review, using highly cited literature from diverse classifications as representative examples  procedures resulted in significant improvements in balance and motor function over CP-treated stroke patients ; and comIn addition, virtual reality is considered to be an efficient adjunctive therapy for the functional recovery of verbal ability in post-stroke aphasic patients , and theMild cognitive impairment (MCI), also referred to as the predementia stage, is one of the most common cognitive dysfunctions seen in the elderly population. Studies have suggested that virtual reality-based cognitive training (VRCT) can promote brain, cognitive, and physical health in older adults with MCI . VR-baseVR has also been proven to be effective in the cognitive and motor rehabilitation of Parkinson’s patients. The corresponding VR cognitive application or training system on the cognitive and behavioral recovery of Parkinson’s patients was able to exercise their memory, executive functions, attention, logical thinking, and speed of thought, thus strengthening their cognitive functions in terms of executive and visuospatial abilities ,43. FurtThe effect of VR on the motor rehabilitation of Parkinson’s patients is also evident. Virtual reality and motion picture training combined with conventional physiotherapy can remarkably improve resting tremors, rigidity, posture, gait, and slow body movements in Parkinson’s patients . A commeTraumatic brain injury (TBI) is a devastating injury that can lead to deficits in multiple domains. Virtual reality combined with treadmill training is safe and feasible for TBI patients. Those who accepted VR balance interventions presented greater enjoyment of training compared to those who participated in conventional therapeutic approaches and those who just used a treadmill . MeanwhiMotion sickness (MS) can be triggered by direct or indirect stimuli due to mismatches in the visual–vestibular autonomic pathways. VR proved to be significantly effective and beneficial for MS rehabilitation. According to the study, the regular and frequent application of visual stimulation in VR games for MS patients has a positive impact on vestibular adaptation mechanisms , improviVirtual reality technology offers immersive training content that is both appealing to children and effective in some neurological disorders in children, such as cerebral palsy and children’s dyslexia. The study demonstrated the feasibility, safety, and initial efficacy of VR-based interactive cognitive training (VICT) systems for executive function rehabilitation in TBI children . VR-baseVR creates a secure environment for patients to experience and explore freely. Patients’ various perceptual activities, such as vision, hearing, and touch, as well as emotional reactions, such as joy, sadness, tension, and fear, can be fully expressed. These technical features of VR are well suited for psychological treatment .In autism spectrum disorder treatment, VR is a proper and promising tool to improve the cognitive function of individuals who are severely affected by autism spectrum disorder . The utiIn depression treatment, VR therapy integrated with neurological rehabilitation has a positive effect on improving mood and reducing depressive symptoms in post-stroke patients , and a fIn schizophrenia treatment, multimodal adaptive social interventions in virtual reality are feasible and acceptable in improving social functioning and clinical outcomes in schizophrenia patients . For exaVR has been applied for pain distraction in a wide range of known painful medical procedures. For example, Oculus Rift VR goggles can assist in pain control in the occupational therapy of pediatric burn patients and can be employed for pain distraction in the rehabilitation of burnt children . AdditioMedical services in cardiopulmonary rehabilitation have been successfully carried out through virtual reality technology, and the specific applications are shown in Regarding cardiovascular rehabilitation, VR, as an assistant tool to conventional cardiac rehabilitation (CR) programs, performs well in promoting compliance and satisfaction in stage II ischemic heart disease patients compared to the conventional treatment group . The useIn lung rehabilitation, an effective improvement can be made in terms of lung function, cognitive function, exercise tolerance, and medication efficiency through VR-based pulmonary rehabilitation training, which can also reduce the symptoms of dyspnea in elderly chronic obstructive pulmonary disease (COPD) patients with mild cognitive dysfunction (MCI) .Rehabilitation was a critical aspect of healthcare systems during the COVID-19 pandemic, and COVID-19 survivors suffered from reduced lung function, critical illness polyneuropathy and myopathy, and cardiorespiratory deconditioning. Therefore, it is important to prepare new interventions that allow healthcare providers to maximize responses to rehabilitation challenges. VR can provide a differentiated form of intervention during hospitalization for COVID-19, and virtual reality software can have a positive impact on the motivation and engagement of COVID-19 patients compared to conventional physical therapy interventions. Apart from in-hospital treatment, cognitive rehabilitation can also be delivered through a remote rehabilitation modality in conjunction with VR . The stuVR also shows good performance in improving patients’ spatial neglect (SN) and is regarded as an effective way to promote visual field recovery, spatial cognition, and mood in patients with unilateral spatial neglect after stroke . SatisfaThe rapid progress of VR technology has introduced a new vision for clinical rehabilitation treatment by providing a new means of rehabilitation, higher treatment compliance, and better patient management in a hospital or home environment, with better efficacy for a wide range of diseases. The application of VR technology will be an important direction in the future development of rehabilitation treatment. At present, some achievements have been attained in the research on VR technology in rehabilitation, but there are still many issues to be solved by rehabilitation experts and engineering experts. Hence, this study presents the following challenges and future perspectives, taking into account the current research focus and topic evolution development.Current VR technology mainly depends on large projection screens or head-mounted displays to generate VR environments. Due to the inconsistency between visual and physical perceived motion, visually induced motion sickness disorder may occur, with symptoms such as headache, sweating, nausea, vomiting, fatigue, and disorientation, and may also cause safety issues and other health problems ,76. MotiA fully immersive VR environment causes the juxtaposition of perception and hallucination, blurring the boundary between reality and hallucination ,78. WhenRehabilitation often requires personalized treatment plans tailored to each patient’s specific condition and progress. VR applications need to be flexible and adaptable to cater to the diverse needs of patients . CustomiIntegrating VR technology into traditional rehabilitation practices can be a complex process. Rehabilitation experts and engineering experts must collaborate to ensure seamless integration of VR technology with existing treatment approaches . This inAt this stage, the sensitivity of most sensors cannot fully meet the rehabilitation needs of patients. It is expected that researchers can develop VR products offering a full range of somatosenses as soon as possible that can give users a full-body experience containing the senses of touch, hearing, smell, and taste. Meanwhile, researchers need to pay attention to how to reduce the discomfort of users’ experience, increase their emotional experience and adjust their emotions, allowing the virtual environment and the real environment to achieve a seamless connection. In addition, VR rehabilitation products also aim to create a virtual entity that integrates initiative, responsiveness, autonomy, sociality, mobility, and adaptability to meet the diversified needs of patients in the aspects of movement, speech, emotion, and social interaction.Currently, VR technology’s application in rehabilitation lacks more standardized treatment guidelines to guide the development of VR rehabilitation programs. More research, especially randomized controlled trials, is still needed in the future to confirm the effectiveness of VR rehabilitation programs.Owing to the high cost of VR equipment, the existing clinical application studies generally have a small sample size of subjects. Moreover, there is variability in the effects of patients applying VR technology; thus, the rehabilitation training conditions are unclear. The effectiveness of its clinical application is still expected to be found in more high-quality studies.This article presents a bibliometric analysis of research on the application of VR in rehabilitation medicine. The main findings are represented in the following aspects.Through the analysis of the temporal distribution graph, this article discovers trends in the research output of the application of VR in rehabilitation medicine. From the initial exploration of how to apply virtual reality in rehabilitation, research on the application of VR in rehabilitation medicine has continued for 30 years and has received growing attention from researchers. Especially after 2013, the number of studies has grown dramatically, and numerous research results have been achieved.The distribution of this research field in the world was confirmed through the analysis of a national  collaboration network. The United States, Italy, Canada, Spain, and China are the major countries for research on the application of VR in rehabilitation medicine, while the United States exceeds other countries in terms of both the number and influence of the literature. Globally, the proportion of multinational and cross-regional collaborations in the research on the application of VR in rehabilitation medicine is increasing, and the research is gradually becoming more specialized, comprehensive, and holistic.Through a keyword co-word timeline network analysis, we find the core literature and topic evolution pathways of the research on the application of VR in rehabilitation medicine. This study divides the research on the application of VR in rehabilitation medicine into three stages: the exploratory stage, the developmental stage, and the promotion application stage. The research content of each stage is related to the technological development at that time.A thematic review of the research on the application of VR in rehabilitation medicine was summarized by analyzing the keyword co-word network. The areas of research focus on the application of VR in rehabilitation medicine are diverse. The research themes in several areas of neurological rehabilitation, psychological treatment, pain distraction, cardiopulmonary rehabilitation, and visual–spatial disorders all reflect the main focuses of research on the application of VR in rehabilitation medicine.Finally, this article presents the current challenges and future prospects for the application of VR in rehabilitation medicine. Overcoming VR-induced motion sickness disorder and mental disorders caused by excessive VR use are both challenges for this research field. Furthermore, developing VR products with better experience, constructing standardized guidelines, and conducting more high-quality clinical studies are all future research trends for the application of VR in rehabilitation medicine.This research systematically sorts and summarizes the relevant research on the application of VR in rehabilitation medicine and provides references for future practice and exploration in this field. However, this study also has limitations. Only the literature in the WOS core dataset was searched and analyzed; thus, the data sample was not comprehensive. Further studies will expand the scope of the literature search for a more comprehensive analysis.