Mihael Srđan Grbić

Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets.

By means of nuclear spin-lattice relaxation rate T(1)(-1), we follow the spin dynamics as a function of the applied magnetic field in two gapped quasi-one-dimensional quantum antiferromagnets: the anisotropic spin-chain system NiCl(2)-4SC(NH(2))(2) and the spin-ladder system (C(5)H(12)N)(2)CuBr(4). In both systems, spin excitations are confirmed to evolve from magnons in the gapped state to spinons in the gapless Tomonaga-Luttinger-liquid state. In between, T(1)(-1) exhibits a pronounced, continuous variation, which is shown to scale in accordance with quantum criticality. We extract the critical exponent for T(1)(-1), compare it to the theory, and show that this behavior is identical in both studied systems, thus demonstrating the universality of quantum-critical behavior.

Field-Induced Quantum Soliton Lattice in a Frustrated Two-Leg Spin-1/2 Ladder

Based on high-field (31)P nuclear magnetic resonance experiments and accompanying numerical calculations, it is argued that in the frustrated S=1/2 ladder compound BiCu(2)PO(6) a field-induced soliton lattice develops above a critical field of μ(0)H(c1)=20.96(7) T. Solitons result from the fractionalization of the S=1, bosonlike triplet excitations, which in other quantum antiferromagnets are commonly known to experience Bose-Einstein condensation or to crystallize in a superstructure. Unlike in spin-Peierls systems, these field-induced quantum domain walls do not arise from a state with broken translational symmetry and are triggered exclusively by magnetic frustration. Our model predicts yet another second-order phase transition at H(c2)>H(c1), driven by soliton-soliton interactions, most likely corresponding to the one observed in recent magnetocaloric and other bulk measurements.

Upper critical field, penetration depth, and depinning frequency of the high-temperature superconductor LafeAsO0.9F0.1 studied by microwave surface impedance

Temperature-dependent and magnetic-field-dependent measurements of the microwave surface impedance of superconducting

Solid-State NMR/NQR and First-Principles Study of Two Niobium Halide Cluster Compounds

{\text{LaFeAsO}}_{0.9}{\text{F}}_{0.1}

Temperature range of superconducting fluctuations above T c in YBa 2 Cu 3 O 7 − δ single crystals

({T}_{c}\ensuremath{\approx}26\text{ }\text{K})

Microwave measurements of the in-plane and c -axis conductivity in HgBa2 CuO4+δ: Discriminating between superconducting fluctuations and pseudogap effects

reveal a very large upper critical field

Microwave study of magnetic field penetration parallel to thin niobium films

({B}_{c2}\ensuremath{\approx}56\text{ }\text{T})

Microscopic properties of the "pinwheel" kagome compound Rb2Cu3SnF12

and a large value of the depinning frequency

Mixed state conductivity of thin niobium films in perpendicular magnetic fields

({f}_{0}\ensuremath{\approx}6\text{ }\text{GHz})