Abstract
In crystalline magnets, interaction randomness is usually thought as a negative factor preventing interesting quantum phenomena to occur. However, intriguing interplay between randomness and quantumness can also leads to unique phenomena in the strongly correlated materials. Among others, the random transverse-field Ising spin chain (RTIC) hosts a renowned quantum Griffiths phase. Although the RTIC model has been regarded as a toy model for long, here we materialize this model with the compound PrTiNbO6, which has a disordered ground state with pronounced quantum fluctuations and continuous spin excitations. The observed anomalous spin dynamics of PrTiNbO6 can be accounted by the RTIC model with a consistent set of parameters determined from fitting the thermodynamic data, and it is ascribed to the quantum Griffiths rare regions in the system. Our results provide a concrete example of quantum Griffiths magnet, and offer an ideal experimental platform for investigating the dynamical properties of random many-body system.
Highlights
Randomness in interactions caused by imperfection is inevitable in solid-state materials
The quantum critical point in uniform quantum Ising chain is strongly modified by the random couplings and fields, into to a quantum Griffiths criticality with divergent dynamical exponent, and the conventional paramagnetic phase turned into a peculiar disordered one with off-critical singularity[12,13,14,15]
Besides the power-law thermodynamics, that the quantum Griffiths singularity is evidenced by the pronounced spin fluctuations and continuous spin excitations at low temperatures
Summary
Randomness in interactions caused by imperfection is inevitable in solid-state materials. The quantum critical point in uniform quantum Ising chain is strongly modified by the random couplings and fields, into to a quantum Griffiths criticality with divergent dynamical exponent, and the conventional paramagnetic phase turned into a peculiar disordered one with off-critical singularity[12,13,14,15]. The exotic quantum Griffiths singularity, with no counterpart in clean systems, has been reported in experiments, including the ferromagnetic alloy Ni1−xVx16,17, thin gallium superconducting films[18], and has been predicted in the randomly layered superfluids[19,20], etc. Besides the power-law thermodynamics, that the quantum Griffiths singularity is evidenced by the pronounced spin fluctuations and continuous spin excitations at low temperatures It turns out the RTIC model, with the parameters determined from fitting the thermodynamic data, can naturally explain the dynamical properties of PrTiNbO6. Spectra in the compound as the locally ordered quantum Griffiths rare region
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