PIRSA:13040133

Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter

Coldea, R. (2013). Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter. Perimeter Institute. https://pirsa.org/13040133

Coldea, Radu. Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter. Perimeter Institute, Apr. 25, 2013, https://pirsa.org/13040133 

          @misc{ pirsa_PIRSA:13040133,
            doi = {10.48660/13040133},
            url = {https://pirsa.org/13040133},
            author = {Coldea, Radu},
            keywords = {Condensed Matter},
            language = {en},
            title = {Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter},
            publisher = {Perimeter Institute},
            year = {2013},
            month = {apr},
            note = {PIRSA:13040133 see, \url{https://pirsa.org}}
          }

Radu Coldea University of Oxford

Talk numberPIRSA:13040133
DOI10.48660/13040133
Collection
Talk Type Conference
Subject

Abstract

Realizing experimentally continuous phase transitions in the electronic ground state of materials near zero temperature as a function of tuning some external parameter (magnetic field, pressure etc.) offers a unique opportunity to probe the extreme regime (near the transition point) where strong quantum correlations encompass the macroscopic sample as a whole, so called “quantum criticality” [1]. In this regime of strong correlations small perturbations/interactions can stabilize novel forms order or collective fluctuations that otherwise do not exist. One of the theoretically most studied paradigms for quantum criticality is a chain of Ising spins driven by a transverse field to a critical point separating spontaneous magnetic order and paramagnetic phases. We have realized this system experimentally by applying strong magnetic fields to the quasi-one-dimensional Ising ferromagnet CoNb2O6 and have probed via single-crystal inelastic neutron scattering the evolution of the magnetic order and spin excitation spectrum as a function of applied field at mili-Kelvin temperatures [2]. Near the critical point the spin excitations were theoretically predicted nearly two decades ago to have a set of quantum resonances (collective modes of vibration of the interacting spins) with universal ratios between their frequencies reflecting an exceptional mathematical structure of the quantum many-body eigenstates with a “hidden” E8 symmetry governing the physics in the scaling limit. Experiments indeed observed evidence for a spectrum of resonances and the ratio between the frequencies of the two lowest modes approached the "golden ratio" near the critical point, as predicted by field theory. As a second example of novel physics near quantum criticality I will discuss how an amplitude-modulated incommensurate spin-density wave (SDW) order appears near the field-induced critical point in the quasi-1D spin-1/2 XY antiferromagnet Cs2CoCl4. Incommensurate SDWs are very uncommon in magnetic insulators and are not stable zero-temperature ground states at the classical mean-field level, we propose that here such a state is stabilized by the strong quantum fluctuations associated with the proximity to the critical point and the weak frustrated inter-chain couplings.