53 research outputs found
Quantum Phase Transition in the One-Dimensional Extended Quantum Compass Model in a Transverse Field
Quantum phase transitions in the one-dimensional extended quantum compass
model in transverse field are studied by using the Jordan-Wigner
transformation. This model is always gapful except at the critical surfaces
where the energy gap disappears. We obtain the analytic expressions of all
critical fields which drive quantum phase transitions. This model shows a rich
phase diagram which includes spin-flop, strip antiferromagnetic and saturate
ferromagnetic phases in addition to the phase with anti parallel ordering of
spin component on odd bonds. However we study the universality and scaling
properties of the transverse susceptibility and nearest-neighbor correlation
functions derivatives in different regions to confirm the results obtained
using the energy gap analysis.Comment: 8 Page, 15 Figure
Numerical study of the one-dimensional quantum compass model
The ground state magnetic phase diagram of the one-dimensional quantum
compass model (QCM) is studied using the numerical Lanczos method. A detailed
numerical analysis of the low energy excitation spectrum is presented. The
energy gap and the spin-spin correlation functions are calculated for finite
chains. Two kind of the magnetic long-range orders, the Neel and a type of the
stripe-antiferromagnet, in the ground state phase diagram are identified. Based
on the numerical analysis, the first and second order quantum phase transitions
in the ground state phase diagram are identified.Comment: 6 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1105.211
Quantum phase transitions in the exactly solved spin-1/2 Heisenberg-Ising ladder
Ground-state behaviour of the frustrated quantum spin-1/2 two-leg ladder with
the Heisenberg intra-rung and Ising inter-rung interactions is examined in
detail. The investigated model is transformed to the quantum Ising chain with
composite spins in an effective transverse and longitudinal field by employing
either the bond-state representation or the unitary transformation. It is shown
that the ground state of the Heisenberg-Ising ladder can be descended from
three exactly solvable models: the quantum Ising chain in a transverse field,
the 'classical' Ising chain in a longitudinal field or the spin-chain model in
a staggered longitudinal-transverse field. The last model serves in evidence of
the staggered bond phase with alternating singlet and triplet bonds on the
rungs of two-leg ladder, which appears at moderate values of the external
magnetic field and consequently leads to a fractional plateau at a half of the
saturation magnetization. The ground-state phase diagram totally consists of
five ordered and one quantum disordered phase, which are separated from each
other either by the lines of discontinuous or continuous quantum phase
transitions. The order parameters are exactly calculated for all five ordered
phases and the quantum disordered phase is characterized through different
short-range spin-spin correlations.Comment: corrected version, figure A1 has been changed, accepted in J. Phys.
A, 19 pages, 7 figure
Quantum Correlation in One-dimensional Extend Quantum Compass Model
We study the correlations in the one-dimensional extended quantum compass
model in a transverse magnetic field. By exactly solving the Hamiltonian, we
find that the quantum correlation of the ground state of one-dimensional
quantum compass model is vanishing. We show that quantum discord can not only
locate the quantum critical points, but also discern the orders of phase
transitions. Furthermore, entanglement quantified by concurrence is also
compared.Comment: 8 pages, 14 figures, to appear in Eur. Phys. J.
Thermodynamic Properties of the One-Dimensional Extended Quantum Compass Model in the Presence of a Transverse Field
The presence of a quantum critical point can significantly affect the
thermodynamic properties of a material at finite temperatures. This is
reflected, e.g., in the entropy landscape S(T; c) in the vicinity of a quantum
critical point, yielding particularly strong variations for varying the tuning
parameter c such as magnetic field. In this work we have studied the
thermodynamic properties of the quantum compass model in the presence of a
transverse field. The specific heat, entropy and cooling rate under an
adiabatic demagnetization process have been calculated. During an adiabatic
(de)magnetization process temperature drops in the vicinity of a field-induced
zero-temperature quantum phase transitions. However close to field-induced
quantum phase transitions we observe a large magnetocaloric effect
Matrix Product State and Quantum Phase Transitions in the One-Dimensional Extended Quantum Compass Model
The matrix product state (MPS) is utilized to study the ground state
properties and quantum phase transitions (QPTs) of the one-dimensional quantum
compass model (QCM). The MPS wavefunctions are argued to be very efficient
descriptions of QCM ground states, and are numerically determined by imaginary
time projections. The ground state energy, correlations, quantum entanglement
and its spectrum, local and nonlocal order parameters, etc., are calculated and
studied in details. It is revealed that the bipartite and block entanglement
entropies, as well as the nearest neighbor correlation functions can be used to
detect the second-order QPTs, but not the first-order ones, while fidelity
detections can recognize both. The entanglement spectrum is extracted from the
MPS wavefunction, and found to be doubly degenerate in disordered phases of
QCM, where non-local string order parameters exist. Moreover, with linearized
tensor renormalization group method, the specific heat curves are evaluated and
their low temperature behaviors are investigated.Comment: 12 pages, 19 figure
From fidelity to entanglement of entropy of the one-dimensional transverse-field quantum compass model
We study fidelity and fidelity susceptibility by addition of entanglement of
entropy in the one-dimensional quantum compass model in a transverse magnetic
field numerically. The whole four recognized gapped regions in the ground state
phase diagram are in the range of our investigation. Power-law divergence at
criticality accompanied by finite size scaling indicates the field induced
quantum phase transitions are of second order as well as from the scaling
behavior of the extremum of fidelity susceptibility is shown the quantum
critical exponents are different in the various regions of phase diagram. We
further calculate a recently proposed quantum information theoretic measure,
von-Neumann entropy, and show that this measure provide appropriate signatures
of the quantum phase transitions (QPT)s occurring at the critical fields.
Von-Neumann entropy indicates a measure of entanglement between some-particle
block and the rest of the system. We show the value of entanglement between a
two-particle block with the rest of the system is more dependent on the power
of exchange couplings connecting the block with the rest of the system than the
power of exchange coupling between two particles in the block
Coupling charge and topological reconstructions at polar oxide interfaces
In oxide heterostructures, different materials are integrated into a single
artificial crystal, resulting in a breaking of inversion-symmetry across the
heterointerfaces. A notable example is the interface between polar and
non-polar materials, where valence discontinuities lead to otherwise
inaccessible charge and spin states. This approach paved the way to the
discovery of numerous unconventional properties absent in the bulk
constituents. However, control of the geometric structure of the electronic
wavefunctions in correlated oxides remains an open challenge. Here, we create
heterostructures consisting of ultrathin SrRuO, an itinerant ferromagnet
hosting momentum-space sources of Berry curvature, and LaAlO, a polar
wide-bandgap insulator. Transmission electron microscopy reveals an atomically
sharp LaO/RuO/SrO interface configuration, leading to excess charge being
pinned near the LaAlO/SrRuO interface. We demonstrate through
magneto-optical characterization, theoretical calculations and transport
measurements that the real-space charge reconstruction modifies the
momentum-space Berry curvature in SrRuO, driving a reorganization of the
topological charges in the band structure. Our results illustrate how the
topological and magnetic features of oxides can be manipulated by engineering
charge discontinuities at oxide interfaces.Comment: 5 pages main text (4 figures), 29 pages of supplementary informatio
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