Quantum spin fluctuations in the spin-liquid state of Tb₂Ti₂O₇

Abstract

Neutron scattering experiments on a polycrystalline sample of the frustrated pyrochlore magnet Tb(2)Ti(2)O(7), which does not show any magnetic order down to 50 mK, have revealed that it shows condensation behavior below 0.4 K from a thermally fluctuating paramagnetic state to a spin-liquid ground state with quantum spin fluctuations. Energy spectra change from quasielastic scattering to a continuum with a double-peak structure at energies of 0 and 0.8 K in the spin-liquid state. Specific heat shows an anomaly at the crossover temperature.

Low-Temperature Low-Field Phases of the Pyrochlore Quantum MagnetTb2Ti2O7

“…Indeed, inelastic neutron scattering suggests a crossover from a thermally disordered paramagnet to a spin liquid at about 0.4 K [13]. But a sharp peak in specific heat, suggestive of long-range ordering, has been observed at 0.37 K by a semi-adiabatic method [11], although no peak has been detected by a relaxation method in a different sample [12].…”

“…In either view, the geometry leads to frustrated nearest-neighbor exchange interactions, whose interplay with an anisotropy dictated by a local <111> direction, dipole-dipole interaction, and quantum fluctuations in some cases, result in various exotic magnetic ground states In Tb 2 Ti 2 O 7 , no long-range order has been found by muon-spin relaxation (µSR) down to 70 mK and by neutron scattering to 50 mK [8,10], two orders of magnitude lower than the absolute value of the crystal-fieldsubtracted Curie-Weiss temperature, about −13 K or −7.0 K [22,23], raising the possibility that this magnet is a long-sought three-dimensional quantum spin liquid. Indeed, inelastic neutron scattering suggests a crossover from a thermally disordered paramagnet to a spin liquid at about 0.4 K [13]. But a sharp peak in specific heat, suggestive of long-range ordering, has been observed at 0.37 K by a semi-adiabatic method [11], although no peak has been detected by a relaxation method in a different sample [12].…”

“…By contrast, Gd 2 Ti 2 O 7 and Er 2 Ti 2 O 7 undergo magnetic transitions at temperatures of the order of 1 K, but their ground states are unconventional, with fluctuations persisting down to 20 mK [6,7]. The most enigmatic are Tb 2 Ti 2 O 7 [8][9][10][11][12][13][14][15][16][17] and Yb 2 Ti 2 O 7 [18][19][20][21], which are under intense investigation.…”

Unusual field dependence of spin fluctuations on different timescales in Tb2Ti2O7

“…8 In addition other work has suggested the existence of quantum spin fluctuations at low temperatures. 22 Another way to distinguish between the theoretical models for the origin of the low temperature fluctuations is to explicitly test one of their predictions. Importantly, when the quantum spin ice model 9 is applied to Tb 2 Ti 2 O 7 it is predicted that for small fields applied along the [111] crystal axis a similar evolution between magnetic states to that in the thoroughly investigated partial magnetization plateaux [24][25][26][27] in Dy 2 Ti 2 O 7 and Ho 2 Ti 2 O 7 will be observed, albeit with a far smaller characteristic field scale, < ∼ 0.1 T. At the lowest temperatures, ≪ 0.1 K, a partial magnetization plateau should be evident 23 in this field region.…”

Spin dynamics in highly frustrated pyrochlore magnets

“…In spite of effective antiferromagnetic interactions leading to a Curie-Weiss temperature of −13 K [48], which should drive the system into long-range order [32,49], prior works pointed out a disordered fluctuating ground state down to 20 mK [50,51]. Various subsequent studies have suggested complex spin dynamics, where different time and temperature scales coexist, as revealed by muons [52][53][54], magnetization [55,56] and neutron scattering experiments [57][58][59][60][61][62][63][64][65][66]. Recently, power law spin correlations have also been reported [67], bearing some resemblance with the pinch point pattern observed in the aforementioned spin ices.…”