Bose-Einstein condensation of triplons in the S = 1 tetramer antiferromagnet K2Ni2(MoO4)3: A compound close to a quantum critical point


Bose-Einstein condensation of triplons in the S = 1 tetramer antiferromagnet K2Ni2(MoO4)3: A compound close to a quantum critical point

Koteswararao, B.; Khuntia, P.; Kumar, R.; Mahajan, A. V.; Yogi, A.; Baenitz, M.; Skourski, Y.; Chou, F. C.

The structure of K2Ni2(MoO4)3 consists of S = 1 tetramers formed by Ni2+ ions. The magnetic susceptibility χ(T ) and specific heat CP (T ) data on a single crystal show a broad maximum due to the low dimensionality of the system with short-range spin correlations. A sharp peak is seen in χ(T ) and CP (T ) at about 1.13 K, well below the broad maximum. This is an indication of magnetic long-range order, i.e., the absence of spin gap in the ground state. Interestingly, the application of a small magnetic field (H >0.1 T) induces magnetic behavior akin to the Bose-Einstein condensation (BEC) of triplon excitations observed in some spin-gap materials. Our results demonstrate that the temperature-field (T -H) phase boundary follows a power law (T − TN) ∝ H1/α with the exponent 1/α close to 2/3 , as predicted for the BEC scenario. The observation of BEC of triplon excitations in small H infers that K2Ni2(MoO4)3 is located in the proximity of a quantum critical point, which separates the magnetically ordered and spin-gap regions of the phase diagram.

Permalink: https://www.hzdr.de/publications/Publ-25675
Publ.-Id: 25675