Field-Driven Quantum Criticality in the Spinel Magnet ZnCr2Se4

Abstract

We report detailed dc and ac magnetic susceptibilities, specific heat, and thermal conductivity measurements on the frustrated magnet ZnCr_{2}Se_{4}. At low temperatures, with an increasing magnetic field, this spinel material goes through a series of spin state transitions from the helix spin state to the spiral spin state and then to the fully polarized state. Our results indicate a direct quantum phase transition from the spiral spin state to the fully polarized state. As the system approaches the quantum criticality, we find strong quantum fluctuations of the spins with behaviors such as an unconventional T^{2}-dependent specific heat and temperature-independent mean free path for the thermal transport. We complete the full phase diagram of ZnCr_{2}Se_{4} under the external magnetic field and propose the possibility of frustrated quantum criticality with extended densities of critical modes to account for the unusual low-energy excitations in the vicinity of the criticality. Our results reveal that ZnCr_{2}Se_{4} is a rare example of a 3D magnet exhibiting a field-driven quantum criticality with unconventional properties.

Magnetic field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr2Se4

“…The maximal value of |∆v/v 0 | reaches 2%, which is ten times larger than the corresponding changes at base temperature and almost two orders of magnitude larger than the spontaneous magnetostriction, suggesting that magnetic interactions exert a much stronger relative effect on the dynamic than static properties of the lattice. The second anomaly that appears in both fielddependence curves around 10 T represents the previously reported high-field transition that was previously associated either with a spin-nematic phase [19] or with a crossover from the quantum-critical region to the fully field-polarized FM phase [22]. The new phase diagram suggested by Gu et al [22] implies a very strong temperature dependence of this high-field anomaly, so that it merges with B c in the zero-temperature limit.…”

“…In the latest study by Gu et al [22], the conical-to-collinear transition has been re-addressed from the point of view of field-driven quantum criticality, which is evidenced by the low-temperature ∝ T 2 behavior of the specific heat and a sharp anomaly in thermal conductivity. In the updated phase diagram, the transition at B c merges with the high-field transition to the field-polarized FM state in the limit T → 0, leading to a well-defined quantum critical point (QCP) and a broad quantum-critical region at elevated temperatures [22].…”

Possible itinerant excitations and quantum spin state transitions in the effective spin-1/2 triangular-lattice antiferromagnet Na2BaCo(PO4)2

“…Thermal conductivity measurements. Thermal conductivity was measured by using a "one heater, two thermometers" technique in a 3 He/ 4 He dilution refrigerator and in a 3 He refrigerator, equipped with a 14 T superconducting magnet [63][64][65][66][67][68][69][70][71][72][73] . The sample was cut precisely along the crystallographic axes with dimensions of 3.0 × 0.63 × 0.14 mm 3 , where the longest and the shortest dimensions are along the a and the c axes, respectively.…”

“…For low-temperature thermal conductivity measurements, calibrating the magnetoresistance effect of resistor thermometers is a basic requirement. The thermometers (RuO 2 ) used at 300 mK to 30 K in the 3 He refrigerator are pre-calibrated by using a capacitance sensor (Lakeshore Cryotronics) as the reference 65 , 67 – 69 ; the thermometers (RuO 2 ) used at 50 mK to 1 K in the dilution refrigerator are pre-calibrated by using a RuO 2 reference sensor (Lakeshore Cryotronics) mounted at the mixture chamber (the superconducting magnet was equipped with a cancellation coil at the height of mixture chamber) 70 – 72 . The resolution of the κ measurements is typically better than 3% (better at higher temperature).…”

Quantum Criticality of Excitonic Insulating Transition in Nodal Line Semimetal ZrSiS

“…In the vicinity of the QCP, the low-energy quasiparticle properties are governed by the quantum fluctuation of order parameter such that some interesting unconventional phenomena could arise, e.g., a significant enhancement or divergence of quasiparticle mass [1]. In real systems, quantum criticality exhibiting greatly enhanced mass has been observed in a variety of materials, including cuprates YBa 2 Cu 3 O 6+δ [2] and Eu(Nd)-LSCO [3], heavy fermion compounds YbRh 2 Si 2 , CeCoIn 5 , and CeRhIn 5 [4][5][6], iron pnictide BaFe(As x P 1−x ) 2 [7], and spinel magnet ZnCr 2 Se 4 [8].…”