15 research outputs found
Anomalous quantum-critical scaling corrections in two-dimensional antiferromagnets
We study the N\'eel-paramagnetic quantum phase transition in two-dimensional
dimerized Heisenberg antiferromagnets using finite-size scaling of
quantum Monte Carlo data. We resolve the long standing issue of the role of
cubic interactions arising in the bond-operator representation when the dimer
pattern lacks a certain symmetry. We find non-monotonic (monotonic) size
dependence in the staggered (columnar) dimerized model, where cubic
interactions are (are not) present. We conclude that there is an irrelevant
field in the staggered model that is not present in the columnar case, but, at
variance with previous claims, it is not the leading irrelevant field. The new
exponent is and the prefactor of the correction
is large and comes with a different sign from that of the
formally leading conventional correction with exponent .
Our study highlights the possibility of competing scaling corrections at
quantum critical points.Comment: 6 pages, 6 figure
Investigating Berezinskii-Kosterlitz-Thouless phase transitions in Kagome spin ice by quantifying Monte Carlo process: Distribution of Hamming distances
We reinvestigate the phase transitions of the Ising model on the Kagome
lattice with antiferromagnetic nearest-neighbor and ferromagnetic
next-nearest-neighbor interactions, which has a six-state-clock spin ice ground
state and two consecutive Berezinskii-Kosterlitz-Thouless (BKT) phase
transitions. Employing the classical Monte Carlo (MC) simulations, the phases
are characterized by the magnetic order parameter, and the critical
temperatures are obtained by the finite-size scaling of related physical
quantities. Moreover, we attempt to gain general information on the phase
transitions from the MC process instead of MC results and successfully extract
the correct transition points with surprisingly high accuracy. Specifically, we
focus on the selected data set of uncorrelated MC configurations and quantify
the MC process using the distribution of two-configuration Hamming distances in
this small data collection. This distribution is more than a quantity that
features different behaviors in different phases but also nicely supports the
same BKT scaling form as the order parameter, from which we successfully
determine the two BKT transition points with surprisingly high accuracy. We
also discuss the connection between the phase transitions and the intrinsic
dimension extracted from the Hamming distances, which is widely used in the
growing field of machine learning and is reported to be able to detect critical
points. Our findings provide a new understanding of the spin ice transitions in
the Kagome lattice and can hopefully be used similarly to identify transitions
in the quantum system on the same lattice with strong frustrations.Comment: 12 figure
Scaling of disorder operator at deconfined quantum criticality
We study scaling behavior of the disorder parameter, defined as the
expectation value of a symmetry transformation applied to a finite region, at
the deconfined quantum critical point in (2+1) in the - model via
large-scale quantum Monte Carlo simulations. We show that the disorder
parameter for U(1) spin rotation symmetry exhibits perimeter scaling with a
logarithmic correction associated with sharp corners of the region, as
generally expected for a conformally-invariant critical point. However, for
large rotation angle the universal coefficient of the logarithmic corner
correction becomes negative, which is not allowed in any unitary conformal
field theory. We also extract the current central charge from the small
rotation angle scaling, whose value is much smaller than that of the free
theory.Comment: 8 pages, 6 figures; v2 improved measurement on disorder operato
Dynamical signature of fractionalization at a deconfined quantum critical point
Deconfined quantum critical points govern continuous quantum phase transitions at which fractionalized (deconfined) degrees of freedom emerge. Here we study dynamical signatures of the fractionalized excitations in a quantum magnet (the easy-plane J-Q model) that realize a deconfined quantum critical point with emergent O(4) symmetry. By means of large-scale quantum Monte Carlo simulations and stochastic analytic continuation of imaginary-time correlation functions, we obtain the dynamic spin-structure factors in the
S
x
and
S
z
channels. In both channels, we observe broad continua that originate from the deconfined excitations. We further identify several distinct spectral features of the deconfined quantum critical point, including the lower edge of the continuum and its form factor on moving through the Brillouin zone. We provide field-theoretical and lattice model calculations that explain the overall shapes of the computed spectra, which highlight the importance of interactions and gauge fluctuations to explain the spectral-weight distribution. We make further comparisons with the conventional Landau O(2) transition in a different quantum magnet, at which no signatures of fractionalization are observed. The distinctive spectral signatures of the deconfined quantum critical point suggest the feasibility of its experimental detection in neutron scattering and nuclear magnetic resonance experiments.First author draf
Emergent O(4) symmetry at the phase transition from plaquette-singlet to antiferromagnetic order in quasi-two-dimensional quantum magnets
Recent experiments [J. Guo et al., Phys. Rev. Lett.124,206602 (2020)] on
thermodynamic properties of the frustrated layered quantum magnet
SrCu(BO) -- the Shastry-Sutherland material -- have provided strong
evidence for a low-temperature phase transition between plaquette-singlet and
antiferromagnetic order as a function of pressure. Further motivated by the
recently discovered unusual first-order quantum phase transition with an
apparent emergent O(4) symmetry of the antiferromagnetic and plaquette-singlet
order parameters in a two-dimensional "checkerboard J-Q" quantum spin model [B.
Zhao et al., Nat. Phys. 15, 678 (2019)], we here study the same model in the
presence of weak inter-layer couplings. Our focus is on the evolution of the
emergent symmetry as the system crosses over from two to three dimensions and
the phase transition extends from strictly zero temperature in two dimensions
up to finite temperature as expected in SrCu(BO). Using quantum
Monte Carlo simulations, we map out the phase boundaries of the
plaquette-singlet and antiferromagnetic phases, with particular focus on the
triple point where these two order phases meet the paramagnetic phase for given
strength of the inter-layer coupling. All transitions are first-order in the
neighborhood of the triple points. We show that the emergent O(4) symmetry of
the coexistence state breaks down clearly when the interlayer coupling becomes
sufficiently large, but for a weak coupling, of the magnitude expected
experimentally, the enlarged symmetry can still be observed at the triple point
up to significant length scales. Thus, it is likely that the plaquette-singlet
to antiferromagnetic transition in SrCu(BO) exhibits remnants of
emergent O(4) symmetry, which should be observable due to additional weakly
gapped Goldstone modes.Comment: 14 pages, 8 figure
Quantum phases of SrCu2(BO3)2 from high-pressure thermodynamics
We report heat capacity measurements of SrCu(BO) under high
pressure along with simulations of relevant quantum spin models and map out the
phase diagram of the material. We find a first-order quantum phase
transition between the low-pressure quantum dimer paramagnet and a phase with
signatures of a plaquette-singlet state below T = K. At higher pressures,
we observe a transition into a previously unknown antiferromagnetic state below
K. Our findings can be explained within the two-dimensional
Shastry-Sutherland quantum spin model supplemented by weak inter-layer
couplings. The possibility to tune SrCu(BO) between the
plaquette-singlet and antiferromagnetic states opens opportunities for
experimental tests of quantum field theories and lattice models involving
fractionalized excitations, emergent symmetries, and gauge fluctuations.Comment: 6 pages + 8 pages supplemental informatio
Zigzag magnetic order in a novel tellurate compound NaNiTeO with = 1 chains
NaNiTeO is a rare example in the transition-metal
tellurate family of realizing an = 1 spin-chain structure. By performing
neutron powder diffraction measurements, the ground-state magnetic structure of
NaNiTeO is determined. These measurements reveal that below
6.8(2) K, the Ni moments form a screwed
ferromagnetic (FM) spin-chain structure running along the crystallographic
axis but these FM spin chains are coupled antiferromagnetically along the
and directions, giving rise to a magnetic propagation vector of = (0,
1/2, 1/2). This zigzag magnetic order is well supported by first-principles
calculations. The moment size of Ni spins is determined to be 2.1(1)
at 3 K, suggesting a significant quenching of the orbital moment
due to the crystalline electric field (CEF) effect. The previously reported
metamagnetic transition near 0.1 T can be understood as a
field-induced spin-flip transition. The relatively easy tunability of the
dimensionality of its magnetism by external parameters makes
NaNiTeO a promising candidate for further exploring various
types of novel spin-chain physics.Comment: 10 pages, 6 figure