TY  - JOUR
AU  - Musshoff, Julian
AU  - Zhang, Guoren
AU  - Koch, Erik
AU  - Pavarini, Eva
TI  - Linear-response description of super-exchange driven orbital-ordering in K2CuF4
JO  - Physical review / B
VL  - 100
IS  - 4
SN  - 0163-1829
CY  - Woodbury, NY
PB  - Inst.
M1  - FZJ-2020-00318
SP  - 045116
PY  - 2019
AB  - We study the nature of orbital and magnetic order in the layered perovskite K2CuF4, and compare to the case of the infinite-layer system KCuF3. To this end, we augment the local-density approximation + dynamical mean-field theory technique with linear-response functions. We explain orbital and magnetic order, and their evolution with increasing pressure. We show that both the tetragonal (ɛT) and the Jahn-Teller (ɛJT) crystal-field splitting play a key role. We find that surprisingly, unlike in KCuF3,ɛT is comparable to, or even larger than, ɛJT; in addition, ɛT is mostly determined by the layered structure itself and by the compression of the K cage, rather than by the deformations of the CuF6 octahedra. Next, we study the nature of orbital order. We calculate the superexchange transition temperature, finding TKK∼300K, a value close to the one for KCuF3. Thus, in K2CuF4 as in KCuF3,TKK is too small to explain the existence of orbital order up to the melting temperature. We show, however, that in the case of the layered perovskite, an additional superexchange mechanism is at work. It is an orbital Zeeman term, ˆhKK, and it is active also above TKK. We show that due to ˆhKK, phases with different types of ordering can coexist at temperatures below TKK. Similar effects are likely to play a role in other layered correlated systems.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000475499700003
DO  - DOI:10.1103/PhysRevB.100.045116
UR  - https://juser.fz-juelich.de/record/872850
ER  -