Medium Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 9
Situational Awareness; Communication Breakdown
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Human Factors; Procedure
I issued Aircraft X a clearance to descend and maintain 13;000; aircraft didn't get the clearance the first time so I issued it again and apparently misspoke and told Aircraft X to maintain 11;000 and missed the read back. When I issued the descent clearance to 13;000; I put a temporary altitude of 13;000 in the data block and a hard altitude of 11;000 in for assigned. I guess when I reissued the descent clearance that may have been why I misspoke. Around that same time; I got a few calls from other aircraft and FAT approach called to tell me they switched runways to send Aircraft X direct ZZZ.I may have gotten distracted as well and didn't catch the mistake. The aircraft descended below the Minimum IFR Altitude (MIA) that is 12;800 for a few seconds before they entered the area that the MIA is 11;000. When I observed the aircraft descending below 13;000; I told Aircraft X 'assigned altitude 13;000'. They didn't respond so I said it again and they said they were correcting. They climbed back up a little; but by then I was able to issue them the descent clearance to 11;000 because they were over the 11;000 MIA box.The only recommendation is to pay closer attention to clearances issued and listen closely for the read back.
Oakland Center Controller reported issuing an incorrect altitude; not catching the read back; then caught it as the aircraft descended below the Minimum IFR Altitude.