اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدHiggs transition from a magnetic Coulomb liquid to a ferromagnet in Yb_2Ti_2O_7
238
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
In a class of frustrated magnets known as spin ice, magnetic monopoles emerge as classical defects and interact via the magnetic Coulomb law. With quantum-mechanical interactions, these magnetic charges are carried by fractionalised bosonic quasi-particles, spinons, which can undergo Bose-Einstein condensation through a first-order transition via the Higgs mechanism. Here, we report evidence of a Higgs transition from a magnetic Coulomb liquid to a ferromagnet in single-crystal Yb2Ti2O7. Polarised neutron-scattering experiments show that the diffuse [111]-rod scattering and pinch-point features which develop on cooling are suddenly suppressed below T_C ~ 0.21 K, where magnetic Bragg peaks and a full depolarisation of the neutron spins are observed with thermal hysteresis, indicating a first-order ferromagnetic transition. Our results are explained on the basis of a quantum spin-ice model, whose high-temperature phase is effectively described as a magnetic Coulomb liquid, while the ground state shows a nearly collinear ferromagnetism with gapped spin excitations.
قيم البحث
اقرأ أيضاً
We study the quantum phase transition from a Dirac spin liquid to an antiferromagnet driven by condensing monopoles with spin quantum numbers. We describe the transition in field theory by tuning a fermion interaction to condense a spin-Hall mass, wh
ich in turn allows the appropriate monopole operators to proliferate and confine the fermions. We compute various critical exponents at the quantum critical point (QCP), including the scaling dimensions of monopole operators by using the state-operator correspondence of conformal field theory. We find that the degeneracy of monopoles in QED3 is lifted and yields a non-trivial monopole hierarchy at the QCP. In particular, the lowest monopole dimension is found to be smaller than that of QED3 using a large $N_f$ expansion where $2N_f$ is the number of fermion flavors. For the minimal magnetic charge, this dimension is $0.39N_f$ at leading order. We also study the QCP between Dirac and chiral spin liquids, which allows us to test a conjectured duality to a bosonic CP$^1$ theory. Finally, we discuss the implications of our results for quantum magnets on the Kagome lattice.
The kagome lattice sits at the crossroad of present research efforts in quantum spin liquids, chiral phases, emergent skyrmion excitations and anomalous Hall effects to name but a few. In light of this diversity, our goal in this paper is to build a
unifying picture of the underlying magnetic degrees-of-freedom on kagome. Motivated by a growing mosaic of materials, we especially consider a broad range of nearest-neighbour interactions consisting of Dzyaloshinskii-Moriya as well as anisotropic ferro$-$ and antiferromagnetic coupling. We present a three-fold mapping on the kagome lattice which transforms the celebrated Heisenberg antiferromagnet and XXZ model onto two lines of time-reversal invariant Hamiltonians. The mapping is exact for classical and quantum spins alike, i.e. it preserves the energy spectrum of the original Heisenberg and XXZ models. As a consequence, at the classical level, all phases have an extensive ground-state degeneracy. These ground states support a variety of phenomena such as ferromagnetically induced pinch points in the structure factor and the possibility for spontaneous scalar chirality. For quantum spin$-1/2$, the XXZ model has been recently shown to be a quantum spin liquid. Applying our three-fold mapping to the XXZ model gives rise to a connected network of quantum spin liquids, centered around a paragon of quantum disorder, namely the Ising antiferromagnet. We show that this quantum disorder spreads over an extended region of the phase diagram at linear order in spin wave theory, which overlaps with the parameter region of Herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$. We conclude this work by discussing the connection of our results to the chiral spin liquids found on kagome with further nearest-neighbour interactions, and to the recently synthesized ternary intermetallic materials.
We report specific heat, resistivity and susceptibility measurements at different temperatures, magnetic fields, and pressures to provide solid evidence of CoS2 being a marginal Fermi liquid. The presence of a tricritical point in the phase diagram o
f the system provides an opportunity to test the spin fluctuation theory with a high limit of accuracy. A magnetic field suppresses the amplitude of the spin fluctuations and recovers conventional Fermi liquid behavior, connecting both states continuously.
We report experimental and numerical evidences that the dynamics of the director of a liquid crystal driven by an electric field close to the critical point of the Freedericksz Transition(FT) is not described by a Landau-Ginzburg (LG) equation as it
is usually done in literature. The reasons are related to the very crude approximations done to obtain this equation, to the finite value of the anchoring energy and to small asymmetries on boundary conditions. We also discuss the difference between the use of LG equation for the statics and the dynamics. These results are useful in all cases where FT is used as an example for other orientational transitions.
If spin liquids have been famously defined by what they are not, i.e. ordered, the past years have seen the frontier between order and spin liquid starting to fade, with a growing number of materials whose low-temperature physics cannot be explained
without co-existence of (partial) magnetic order and spin fluctuations. Here we study an example of such co-existence in the presence of magnetic dipolar interactions, related to spin ice, where the order is long range and the fluctuations support a Coulomb gauge field. Topological defects are effectively coupled via energetic and entropic Coulomb interactions, the latter one being stronger than for the spin-ice ground state. Depending on whether these defects break the divergence-free condition of the Coulomb gauge field or the long-range order, they are respectively categorized as monopoles - as in spin ice - or monopole holes, in analogy with electron holes in semiconductors. The long-range order plays the role of a fully-occupied valence band, while the Coulomb spin liquid can be seen as an empty conducting band. These results are discussed in the context of other lattices and models which support a similar co-existence of Coulomb gauge field and long-range order. We conclude this work by explaining how dipolar interactions lift the spin liquid degeneracy at very low energy scale by maximizing the number of flippable plaquettes, in light of the equivalent quantum dimer model.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
