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R. A. Borzi

Publications and source records attributed to R. A. Borzi.

28 records · Page 2Linked to original sources

Quantum oscillations in the anomalous phase in Sr3Ru2O7

We report measurements of quantum oscillations detected in the putative nematic phase of Sr3Ru2O7. Significant improvements in sample purity enabled the resolution of small amplitude dHvA oscillations between two first order metamagnetic transitions delimiting the phase. Two distinct frequencies were observed, and their amplitudes follow the normal Lifshitz-Kosevich profile. The Fermi surface sheets seem to correspond to a subset of those detected outside the phase. Variations of the dHvA frequencies are explained in terms of a chemical potential shift produced by reaching a peak in the density of states, and an anomalous field dependence of the oscillatory amplitude provides information on domains.

cond-mat.str-el↗

Microscopic theory of the nematic phase in Sr$_3$Ru$_2$O$_7$

In an externally applied magnetic field, ultra-pure crystals of the bilayer compound Sr$_3$Ru$_2$O$_7$ undergo a metamagnetic transition below a critical temperature, $T^*$, which varies as a function of the angle between the magnetic field $H$ and the Ru-O planes. Moreover, $T^*$ approaches zero when $H$ is perpendicular to the planes. This putative "metamagnetic quantum critical point", however, is preempted by a nematic fluid phase with order one resistive anisotropy in the {\it ab} plane. In a "realistic" bilayer model with moderate strength local Coulomb interactions, the existence of a sharp divergence of the electronic density of states near a van Hove singularity of the quasi-one-dimensional bands, and the spin-orbit couplings permitted by the presence of multiple orbitals result in a mean-field phase diagram which accounts for many of these experimentally observed phenomena. Although the spin-orbit coupling is not overly strong, it destroys the otherwise near perfect Fermi surface nesting and hence suppresses spin-density-wave (SDW) ordering.

cond-mat.str-el↗

De Haas-van Alphen oscillations in the charge-density wave compound lanthanum tritelluride (LaTe_3)

De Haas-van Alphen oscillations were measured in lanthanum tritelluride (LaTe_3) to probe the partially gapped Fermi surface resulting from charge density wave (CDW) formation. Three distinct frequencies were observed, one of which can be correlated with a FS sheet that is unaltered by CDW formation. The other two frequencies arise from FS sheets that have been reconstructed in the CDW state.

cond-mat.str-el↗

Interplay between thermal percolation and jamming upon dimer adsorption on binary alloys

Using Monte Carlo simulations we study jamming and percolation processes upon the random sequential adsorption of dimers on binary alloys with different degrees of structural order. We obtain the equimolar mixtures used as substrates by applying the isomorphism between an alloy and the Ising model (conserved order parameter). The annealing temperature $T$ of the mixture then is a continuous parameter that characterizes the different sets of substrates, shaping the deposition process. As the alloy undergoes an order-disorder phase transition at the Onsager critical temperature ($T_{c}$), the jamming and percolating properties of the dimers deposited over the substrate are subjected to non-trivial changes. These are reflected in a density-temperature phase diagram with three well-defined regions. We find that for $T < T^* = 1.22 T_{c}$ the occurrence of jamming prevents the onset of percolating clusters, while percolation is possible for $T > T^{*}$. Particular attention is focused close to $T^{*}$, where the interplay between jamming and percolation restricts fluctuations, forcing exponents seemingly different from the standard percolation universality class. By analogy with a thermal transition, we study the onset of percolation by using the {\it temperature} (in this case, the substrate annealing temperature) as a control parameter. By proposing thermal scaling Ansatzes we analyze the behavior of the percolation threshold and its thermally induced fluctuations. Also, the fractal dimension of the percolating cluster is determined. Based on these measurements and the excellent data collapsing, we conclude that the universality class of standard percolation is preserved for all temperatures.

cond-mat.stat-mech↗

Formation of a Nematic Fluid at High Fields in Sr3Ru2O7

In principle, a complex assembly of strongly interacting electrons can self-organise into a wide variety of collective states, but relatively few such states have been identified in practice. We report that, in the close vicinity of a metamagnetic quantum critical point, high purity Sr3Ru2O7 possesses a large magnetoresistive anisotropy, consistent with the existence of an electronic nematic fluid. We discuss a striking phenomenological similarity between our observations and those made in high purity two-dimensional electron fluids in GaAs devices.

cond-mat.str-el↗

Phase Bifurcation and Quantum Fluctuations in Sr3Ru2O7

The bilayer ruthenate Sr_3Ru_2O_7 has been cited as a textbook example of itinerant metamagnetic quantum criticality. However, recent studies of the ultra-pure system have revealed striking anomalies in magnetism and transport in the vicinity of the quantum critical point. Drawing on new experimental data, we propose that the anomalous phase behavior can be accommodated by a mechanism which relies on the effects of strong magnetoelastic coupling. We argue that the phenomenological theory identified here is more generic and raises the possibility of quantum tricritical behaviour.

cond-mat.str-el↗

The de Haas-van Alphen effect across the metamagnetic transition in Sr$_3$Ru$_2$O$_7$

We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant metamagnet Sr$_3$Ru$_2$O$_7$. Extremely high sample purity allows the observation of dHvA oscillations both above and below the metamagnetic transition field of 7.9 T. The quasiparticle masses are fairly large away from the transition, and are enhanced by up to an extra factor of three as the transition is approached, but the Fermi surface topography change is quite small. The results are qualitatively consistent with a field-induced Stoner transition in which the mass enhancement is the result of critical fluctuations.

cond-mat.str-el↗

Rigid-Band Shift of the Fermi Level in a Strongly Correlated Metal: Sr(2-y)La(y)RuO(4)

We report a systematic study of electron doping of Sr2RuO4 by non-isovalent substitution of La^(3+) for Sr^(2+). Using a combination of de Haas-van Alphen oscillations, specific heat, and resistivity measurements, we show that electron doping leads to a rigid-band shift of the Fermi level corresponding to one doped electron per La ion, with constant many-body quasiparticle mass enhancement over the band mass. The susceptibility spectrum is substantially altered and enhanced by the doping but this has surprisingly little effect on the strength of the unconventional superconducting pairing.

cond-mat.str-el↗

Multiple first-order metamagnetic transitions and quantum oscillations in ultrapure

We present measurements on ultra clean single crystals of the bilayered ruthenate metal Sr3Ru2O7, which has a magnetic-field-tuned quantum critical point. Quantum oscillations of differing frequencies can be seen in the resistivity both below and above its metamagnetic transition. This frequency shift corresponds to a small change in the Fermi surface volume that is qualitatively consistent with the small moment change in the magnetisation across the metamagnetic transition. Very near the metamagnetic field, unusual behaviour is seen. There is a strong enhancement of the resistivity in a narrow field window, with a minimum in the resistivity as a function of temperature below 1 K that becomes more pronounced as the disorder level decreases. The region of anomalous behaviour is bounded at low temperatures by two first-order phase transitions. The implications of the results are discussed. PACS: 68.35.Rh, 71.27.+a, 72.15.-v, 74.70.Pq

cond-mat.str-el↗

Angular dependence of the magnetic susceptibility in the itinerant metamagnet Sr3Ru2O7

We report the results of a study of the di erential magnetic susceptibility of Sr3Ru2O7 as a function of temperature and magnetic elds applied at a series of angles to the ab plane. By analysing the real and imaginary parts of the susceptibility, we conclude that the eld angle acts as a continuous tuning parameter for the critical end-point to a line of rst order metamagnetic phase transitions. The end-point sits at approximately 1.25K for elds applied in the ab plane, and is depressed to below 50 mK when the eld is aligned within 10 of the c axis.

cond-mat.str-el↗