Related papers: Quantum disordered phase in a doped antiferromagne…
In presence of dissipation, quantal states may acquire complex-valued phase effects. We suggest a notion of dissipative interferometry that accommodates this complex-valued structure and that may serve as a tool for analyzing the effect of…
Experimental challenges in identifying various types of magnetic ordering in graphene quantum dots (QDs) pose a major hurdle in the application of these nanostructures for spintronic devices. }Based upon phase diagrams obtained by employing…
The ground state (GS) properties of the quasi-one-dimensional $AB_2$ Hubbard model are investigated taking the effects of charge and spin quantum fluctuations on equal footing. In the strong-coupling regime, we derive a low-energy…
We describe four phases found in two-dimensional quantum antiferromagnets. Two of them display long range order at T=0: the N\'eel state and the Valence Bond Crystal. The last two are Spin-Liquids. Properties of these different states are…
We investigate the role of disorder for field-driven quantum phase transitions of metallic antiferromagnets. For systems with sufficiently low symmetry, the combination of a uniform external field and non-magnetic impurities leads…
We propose a new type of magnetically disordered ground state for a frustrated quantum antiferromagnet. This disordered state is an array of spin singlets spontaneously formed on four spin plaquettes. Both perturbation results and…
For the frustrated two-dimensional $S=1/2$ antiferromagnetic Heisenberg model close to quantum phase transition we consider the singlet ground states retaining both translational and SU(2) symmetry. Besides usually discussed checkerboard,…
We propose a universal non-linear sigma model field theory for one dimensional frustrated ferromagnets, which applies in the vicinity of a "quantum Lifshitz point", at which the ferromagnetic state develops a spin wave instability. We…
We discuss the problem of characterizing "quantum disordered" ground states, obtained upon loss of antiferromagnetic order on general lattices in two spatial dimensions, with arbitrary electronic band structure. A key result is the response…
We study the coupled-top model with three large spins located on a triangle. Depending on the coupling strength, there exist three phases: disordered paramagnetic phase, ferromagnetic phase, and frustrated antiferromagnetic phase, which can…
We investigate the spatially anisotropic square lattice quantum antiferromagnet. The model describes isotropic spin-1/2 Heisenberg chains (exchange constant J) coupled antiferromagnetically in the transverse (J_\perp) and diagonal…
Based on an effective Lagrangian obtained from the holon-pair boson theory of Lee and Salk [Phys. Rev. B {\bf 64}, 052501 (2001)] for high $T_c$ cuprates, we explore physical states involved with quantum phase transitions around a critical…
These are lectures presented at the summer course on ``Low Dimensional Quantum Field Theories for Condensed Matter Physicists'', 24 Aug. to 4 Sep. 1992, Trieste, Italy. I review recent work, performed in collaboration primarily with N. Read…
Novel ground-state spin structures in undoped and lightly-doped manganites are here investigated based on the orbital-degenerate double-exchange model, by using mean-field and numerical techniques. In undoped manganites, a new…
The quantum phase transition between paramagnetic and antiferromagnetic phases of the Kondo lattice model with Ising anisotropy in the intersite exchange is studied within the framework of extended dynamical mean-field theory.…
Quantum antiferromagnets on geometrically frustrated lattices have long attracted interest for the formation of quantum disordered states and the possible emergence of quantum spin liquid (QSL) ground states. Here we turn to the…
Spin-state transitions, observed in many transition metal compounds containing Co$^{3+}$ and Fe$^{2+}$, may occur with the change of temperature, pressure, but also with doping, in which case the competition of single-site effects and…
The pseudogap effect of underdoped high-$T_c$ superconductors is studied in the U(1) gauge theory of the t-J model including the spinon pairing fluctuation. The gauge fluctuation breaks the long range correlation between the spinon pairs.…
We use density matrix renormalization group to study the first-order quantum phase transition induced by a magnetic field $h$ in a frustrated ferrimagnetic chain. The magnetization ($m$) curve as a function of $h$ presents a macroscopic…
We study a classical double exchange magnet with direct antiferromagnetic superexchange coupling, J, between the localized spins. It is shown that the de-stabilization of the ferromagnetic ground state with increasing J leads to phase…