arXiv subjects

S. Rosenkranz

Publications and source records attributed to S. Rosenkranz.

61 records · Page 4Linked to original sources

arXiv2002

Crossover from coherent to incoherent electronic excitations in the normal state of Bi2Sr2CaCu2O8

Angle resolved photoemission spectroscopy (ARPES) and resistivity measurements are used to explore the overdoped region of the high temperature superconductor Bi2Sr2CaCu2O8+delta. We find evidence for a new crossover line in the phase diagram between a coherent metal phase for lower temperatures and higher doping, and an incoherent metal phase for higher temperatures and lower doping. The former is characterized by two well-defined spectral peaks in ARPES due to coherent bilayer splitting and superlinear behavior in the resistivity, whereas the latter is characterized by a single broad spectral feature in ARPES and a linear temperature dependence of the resistivity.

cond-mat.supr-con↗

arXiv2002

Spontaneous time reversal symmetry breaking in the pseudogap state of high-Tc superconductors

When matter undergoes a phase transition from one state to another, usually a change in symmetry is observed, as some of the symmetries exhibited are said to be spontaneously broken. The superconducting phase transition in the underdoped high-Tc superconductors is rather unusual, in that it is not a mean-field transition as other superconducting transitions are. Instead, it is observed that a pseudo-gap in the electronic excitation spectrum appears at temperatures T* higher than Tc, while phase coherence, and superconductivity, are established at Tc (Refs. 1, 2). One would then wish to understand if T* is just a crossover, controlled by fluctuations in order which will set in at the lower Tc (Refs. 3, 4), or whether some symmetry is spontaneously broken at T* (Refs. 5-10). Here, using angle-resolved photoemission with circularly polarized light, we find that, in the pseudogap state, left-circularly polarized photons give a different photocurrent than right-circularly polarized photons, and therefore the state below T* is rather unusual, in that it breaks time reversal symmetry11. This observation of a phase transition at T* provides the answer to a major mystery of the phase diagram of the cuprates. The appearance of the anomalies below T* must be related to the order parameter that sets in at this characteristic temperature .

cond-mat.str-el↗

arXiv2001

Magnetic Resonance, Electronic spectra and Bilayer Splitting in Underdoped Bi2212

We report the first inelastic neutron scattering (INS) experiments of the resonance in the underdoped regime of Bi2Sr2CaCu2O8+d. The energy of the resonance is found to be 34 meV and the temperature dependence shows a smooth evolution through Tc with a remnant persisting in the pseudogap state. Besides the INS data, we present also angle resolved photoemission (ARPES) spectra taken on the same crystals. As a function of temperature, the neutron intensity scales with the square of the ARPES gap estimated by the leading-edge midpoint at (pi,0). We also show that the energy of the collective mode inferred from the peak-dip-hump structure compares well with the energy of the resonance. Based on kinematics, we argue that the correlation of these two energies is consistent with the absence of bilayer splitting in the electronic dispersion.

cond-mat.supr-con↗

arXiv1999

Observation of Kosterlitz-Thouless spin correlations in the colossally magnetoresistive layered manganite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$

The spin correlations of the bilayer manganite $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$ have been studied using neutron scattering. On cooling within the paramagnetic state, we observe purely two-dimensional behavior with a crossover to three-dimensional scaling close to the ferromagnetic transition. Below $T_C$, an effective finite size behavior is observed. The quantitative agreement of these observations with the conventional quasi two-dimensional Kosterlitz-Thouless model indicates that the phase transition is driven by the growth of magnetic correlations, which are only weakly coupled to polarons above $T_C$.

cond-mat.str-el↗

arXiv1999

Charge melting and polaron collapse in $La_{1.2}Sr_{1.8}Mn_{2}O_{7}$

X-ray and neutron scattering measurements directly demonstrate the existence of polarons in the paramagnetic phase of optimally-doped colossal magnetoresistive oxides. The polarons exhibit short-range correlations that grow with decreasing temperature, but disappear abruptly at the ferromagnetic transition because of the sudden charge delocalization. The "melting" of the charge ordering as we cool through $T_C$ occurs with the collapse of the quasi-static polaron scattering, and provides important new insights into the relation of polarons to colossal magnetoresistance.

cond-mat.str-el↗

arXiv1999

Ising pyrochlore magnets: Low temperature properties, ice rules and beyond

Pyrochlore magnets are candidates for spin-ice behavior. We present theoretical simulations of relevance for the pyrochlore family R2Ti2O7 (R= rare earth) supported by magnetothermal measurements on selected systems. By considering long ranged dipole-dipole as well as short-ranged superexchange interactions we get three distinct behaviours: (i) an ordered doubly degenerate state, (ii) a highly disordered state with a broad transition to paramagnetism, (iii) a partially ordered state with a sharp transition to paramagnetism. Thus these competing interactions can induce behaviour very different from conventional ``spin ice''. Closely corresponding behaviour is seen in the real compounds---in particular Ho2Ti2O7 corresponds to case (iii) which has not been discussed before, rather than (ii) as suggested earlier.

cond-mat.stat-mech↗

arXiv1997

Neutron scattering investigation of magnetic bilayer correlations in $La_{1.2}Sr_{1.8}Mn_2O_7$

Neutron scattering investigations of the paramagnetic correlations in the layered manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$, which exhibits colossal magnetoresistance above the Curie transition at T$_C$ = 112 K, show that spins in neighboring layers within each bilayer are strongly canted at an average angle that is dependent on both the magnetic field and temperature, as predicted by de Gennes. The in-plane correlation length does not diverge at T$_C$, although the magnetic Bragg intensity obeys critical scaling below T$_C$, with the same temperature dependence as the zero-field electrical conductance.

cond-mat.str-el↗