The control of antiferromagnets with ultrashort optical pulses has emerged as a prominent field research. Tailored laser excitation can launch coherent spin waves at terahertz frequencies, yet comprehensive description their generation mechanisms is still lacking despite extensive efforts. Using emission spectroscopy, we investigate the magnon mode in van der Waals antiferromagnet NiPS_{3} under range photoexcitation conditions. By tuning pump photon energy from transparency to resonant d-d...

In two dimensions, the topological order described by ${\mathbb{Z}}_{2}$ gauge theory coupled to free or weakly interacting fermions with a nonzero spectral Chern number $\ensuremath{\nu}$ is classified $\ensuremath{\nu}\phantom{\rule{0.28em}{0ex}}\mathrm{mod}\phantom{\rule{0.28em}{0ex}}16$ as predicted Kitaev [Ann. Phys. 321, 2 (2006)]. Here, we provide systematic and complete construction of microscopic models realizing this so-called sixteenfold way anyon theories. These are defined...

Abstract Quantum fluctuations can inhibit long-range ordering in frustrated magnets and potentially lead to quantum spin liquid (QSL) phases. A prime example are gapless QSLs with emergent U(1) gauge fields, which have been understood be described terms of electrodynamics 2+1 dimension (QED 3 ). Despite several promising candidate materials, however, a complicating factor for their realisation is the presence other degrees freedom. In particular lattice distortions act relieve magnetic...

Fractionalized Fermi liquids (${\mathrm{FL}}^{*}$) have been introduced as non-Fermi-liquid metallic phases, characterized by coexisting electron-like charge carriers and local moments which form a fractionalized spin liquid. Here we investigate Kondo lattice model on the honeycomb with Kitaev interactions among moments, concrete hosting ${\mathrm{FL}}^{*}$ phases based Kitaev's ${\mathbb{Z}}_{2}$ We characterize via perturbation theory, employ Majorana-fermion mean-field theory to map out...

We study transitions between topological phases featuring emergent fractionalized excitations in two-dimensional models for Mott insulators with spin and orbital degrees of freedom. The realize fermionic quantum critical points Gross-Neveu* universality classes ($2+1$) dimensions. They are characterized by the same set exponents as their ordinary Gross-Neveu counterparts, but feature a different energy spectrum, reflecting nontrivial topology adjacent phases. exemplify this square-lattice...

Moiré heterostructures of transition metal dichalcogenides (TMDs) exhibit Mott-insulating behavior both at half filling as well fractional fillings, where electronic degrees freedom form self-organized Wigner crystal states. An open question concerns magnetic states obtained by lifting the pseudospin-1/2 degeneracy these lowest temperatures. While virtual hopping is expected to induce (weak) antiferromagnetic exchange interactions, are strongly suppressed when considering dilute fractions....

Spin-orbital liquids are quantum disordered states in systems with entangled spin and orbital degrees of freedom. We study exactly solvable spin-orbital models two dimensions selected Heisenberg-, Kitaev-, $\mathrm{\ensuremath{\Gamma}}$-type interactions, as well external magnetic fields. These realize a variety spin-orbital-liquid phases featuring dispersing Majorana fermions Fermi surfaces, nodal Dirac or quadratic band touching points, full gaps. In particular, we show that Zeeman fields...

We investigate the phase diagram of a bilayer Kitaev honeycomb model with Ising interlayer interactions, deriving effective models via perturbation theory and performing Majorana mean-field calculations. show that diverse array magnetic topological transitions occur, depending on direction interaction relative sign interactions. When two layers have same interaction, first-order transition from spin liquid to magnetically ordered state takes place. The order points along axis it is...

The interplay of topological electronic band structures and strong interparticle interactions provides a promising path towards the constructive design robust, long-range entangled many-body systems. As prototype for such systems, we here study an exactly integrable, local model fractionalized insulator. Using controlled perturbation theory about this limit, demonstrate existence bands zeros in exact fermionic Green’s function show that they do affect invariant system, but not quantized...

Optical pump-probe experiments carried out in the time domain reveal both intrinsic low-energy dynamics and its connections to higher-energy excitations correlated electron systems. In this work, we propose two microscopic mechanisms for optical generation of coherent magnetic modes van der Waals magnets, derive corresponding effective light-spin interactions: either through pumping atomic orbital resonantly or via a light-induced Floquet spin Hamiltonian, ground state system is driven...

Kitaev's honeycomb-lattice spin-$1/2$ model has become a paradigmatic example for $\mathbb{Z}_2$ quantum spin liquids, both gapped and gapless. Here we study the fate of these spin-liquid phases in differently stacked bilayer versions Kitaev model. Increasing ratio between inter-layer Heisenberg coupling $J_\perp$ intra-layer couplings $K^{x,y,z}$ destroys topological liquid favor paramagnetic dimer phase. We phase diagrams as function $J_\perp/K$ anisotropies using Majorana-fermion...

Emergent gauge theories take a prominent role in the description of quantum matter, supporting deconfined phases with topological order and fractionalized excitations. A common construction \mathbb{Z}_2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>ℤ</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> lattice theories, first introduced by Wegner, involves Ising spins placed on links subject to discrete Gauss law constraint. As shown Kitaev, also...

The decohering environment of a quantum bit is often described by the coupling to large bath spins. itself can be seen as spin $S=\frac{1}{2}$ which commonly called central spin. resulting model describes an important mechanism decoherence. We provide mathematically rigorous bounds for persisting magnetization in this with and without magnetic field. In particular, we show that there well-defined limit infinite number Only if fraction very weakly coupled spins tends 100% does no persist.

Recent numerical results [Gonzalez et al., Phys. Rev. Lett. 122, 017201 (2019); Shimada J. Conf. Ser. 969, 012126 (2018)] point to the existence of a partial-disorder ground state for spin-1/2 antiferromagnet on stuffed honeycomb lattice, with 2/3 local moments ordering in an antiferromagnetic N\'eel pattern, while remaining 1/3 sites display short-range correlations only, akin quantum spin liquid. We derive effective model this disordered subsystem, by integrating out fluctuations ordered...

In this work, we study a slave-rotor mean-field theory of an extended Hubbard model, applicable to transition metal dichalcogenide moir\'e systems, that captures both the formation Wigner crystals as well exotic spin states on top these charge backgrounds. Phase diagrams are mapped out for different choices long-range Coulomb repulsion strength, reproducing several experimentally found crystal states. Assuming unbroken time-reversal symmetry, find spin-liquid dimer at fractional fillings....

In a collinear antiferromagnet, spins tend to cant towards the direction of an applied magnetic field, thereby decreasing energy system. The canting angle becomes negligible when field is small so that induced anisotropic substantially lower than exchange energy. However, this tiny anisotropy can play significant role intrinsic antiferromagnet small. our work, we conduct direct imaging N\'eel vector in two-dimensional easy-plane MnPSe$_3$, with spin under external in-plane field. inherent...

The $S=1$ bilinear-biquadratic Heisenberg exchange model on the triangular lattice with a single-ion anisotropy has previously been shown to host number of exotic magnetic and nematic orders [Moreno-Cardoner et al., Phys. Rev. B 90, 144409 (2014)], including an extensive region ``supersolid'' order. In this work, we amend by $XXZ$ in interactions. Tuning limit exactly solvable generalized Ising-/Blume-Capel-type provides controlled access phases at finite transverse exchange. Notably, find...

We study the zero-temperature phase diagrams of Majorana-Hubbard models with $\mathrm{SO}(N$) symmetry on two-dimensional honeycomb and $\ensuremath{\pi}$-flux square lattices, using mean-field renormalization group approaches. The can be understood as real counterparts $\mathrm{SU}(N$) Hubbard-Heisenberg may realized in Abrikosov vortex phases topological superconductors, or fractionalized strongly frustrated spin-orbital magnets. In weakly interacting limit, feature stable fully symmetric...

When two layers of two-dimensional materials are assembled with a relative twist, moir\'e patterns arise, inducing tremendous wealth exotic phenomena. In this work, we consider twisting triangular lattices hosting Dirac quantum spin liquids. A single decoupled layer is described by compact electrodynamics in 2+1 dimensions (QED$_3$) an emergent $\mathrm{U}(1)$ gauge field, which assumed to flow strongly interacting fixed point the IR conformal symmetry. We use recent results for numbers...

Emergent gauge theories take a prominent role in the description of quantum matter, supporting deconfined phases with topological order and fractionalized excitations. A common construction $\mathbb{Z}_2$ lattice theories, first introduced by Wegner, involves Ising spins placed on links subject to discrete Gauss law constraint. As shown Kitaev, also emerge exact solution certain spin systems bond-dependent interactions. In this context, field is constructed from Majorana fermions,...

We study the interaction of a (classical) light field with magnetic degrees freedom in two-dimensional antiferromagnet Sr$_2$IrO$_4$. The reduced space group symmetry crystal allows for several channels spin-operator bilinears to couple electric field. Integrating out high-energy Keldysh framework, we derive induced effective fields which enter equations motion low-energy mode in-plane rotations out-of-plane magnetization. Considering pump-probe protocol, these excite magnetization...

A complicating factor in the realization and observation of quantum spin liquids materials is ubiquitous presence other degrees freedom, particular lattice distortion modes (phonons). These provide additional routes for relieving magnetic frustration, thereby possibly destabilizing spin-liquid ground states. In this work, we focus on triangular-lattice Heisenberg antiferromagnets, where recent numerical evidence suggests an extended U(1) Dirac liquid phase which described by compact...

The control of antiferromagnets with ultrashort optical pulses has emerged as a prominent field research. Tailored laser excitation can launch coherent spin waves at terahertz frequencies, yet comprehensive description their generation mechanisms is still lacking despite extensive efforts. Using emission spectroscopy, we investigate the magnon mode in van der Waals antiferromagnet NiPS$_3$ under range photoexcitation conditions. By tuning pump photon energy from transparency to resonant...

Deconfined quantum critical points (DQCPs) are putative phase transitions beyond the Landau paradigm with emergent fractionalized degrees of freedom. The original example a DQCP is spin-1/2 antiferromagnet on square lattice which features second order transition between valence bond solid (VBS) and N\'eel order. VBS breaks symmetry, corresponding parameter may couple to distortion modes (phonons) at appropriate momenta. We investigate field-theoretic description in presence such spin-lattice...