589 research outputs found
Effect of nonmagnetic dilution in honeycomb lattice iridates NaIrO and LiIrO
We have synthesized single crystals of Na(IrTi)O and
polycrystals of Li(IrTi)O and studied the effect of
magnetic depletion on the magnetic properties by measurements of the magnetic
susceptibility, specific heat and magnetocaloric effect at temperatures down to
0.1~K. In both systems, the non-magnetic substitution rapidly changes the
magnetically ordered ground state into a spin glass, indicating strong
frustration. While for the Li system the Weiss temperature
remains unchanged up to , a strong decrease is found
for the Na system. This suggests that only for the former system magnetic
exchange beyond nearest neighbors is dominating. This is also corroborated by
the observation of a smeared quantum phase transition in
Li(IrTi)O near , i.e. much beyond the site
percolation threshold of the honeycomb lattice.Comment: 8 pages including supplemental, 12 figure
Zero-field Quantum Critical Point in CeCoIn
Quantum criticality in the normal and superconducting state of the
heavy-fermion metal CeCoIn is studied by measurements of the magnetic
Gr\"{u}neisen ratio, , and specific heat in different field
orientations and temperatures down to 50 mK. Universal temperature over
magnetic field scaling of in the normal state indicates a hidden
quantum critical point at zero field. Within the superconducting state the
quasiparticle entropy at constant temperature increases upon reducing the field
towards zero, providing additional evidence for zero-field quantum criticality.Comment: submitted to PR
Spin liquid close to a quantum critical point in NaIrO
NaIrO is a candidate material for a 3-dimensional quantum
spin-liquid on the hyperkagome lattice. We present thermodynamic measurements
of heat capacity and thermal conductivity on high quality
polycrystalline samples of NaIrO down to mK and mK,
respectively. Absence of long-range magnetic order down to mK strongly
supports claims of a spin-liquid ground state. The constant magnetic
susceptibility below K and the presence of a small but
finite linear- term in suggest the presence of gapless spin
excitations. Additionally, the magnetic Grneisen ratio shows a
divergence as K and a scaling behavior which clearly
demonstrates that NaIrO is situated close to a zero-field QCP.Comment: 5 pages, 4 figures, PRB rapid, in pres
Uniform Mixing of High-Tc Superconductivity and Antiferromagnetism on a Single CuO2 Plane in Hg-based Five-layered Cuprate
We report a site selective Cu-NMR study on under-doped Hg-based five-layered
high- cuprate HgBa2Ca4Cu5Oy with a Tc=72 K. Antiferromagnetism (AF)
has been found to take place at TN=290 K, exhibiting a large antiferromagnetic
moment of 0.67-0.69uB at three inner planes (IP's). This value is comparable to
the values reported for non-doped cuprates, suggesting that the IP may be in a
nearly non-doped regime. Most surprisingly, the AF order is also detected with
M(OP)=0.1uB even at two outer planes (OP's) that are responsible for the onset
of superconductivity (SC). The high-Tc SC at Tc = 72 K can uniformly coexist on
a microscopic level with the AF at OP's. This is the first microscopic evidence
for the uniform mixed phase of AF and SC on a single CuO2 plane in a simple
environment without any vortex lattice and/or stripe order.Comment: 4 pages, 4 figures. To be published in Phys.Rev.Let
Quantum criticality near the upper critical field of CePdIn
We report low-temperature specific heat measurements in magnetic fields up to
12 T applied parallel and perpendicular to the tetragonal c-axis of the heavy
fermion superconductor CePdIn. In contrast to its quasi-two-dimensional
(2D) relative CeCoIn, the system displays an almost isotropic upper
critical field. While there is no indication for a FFLO phase in
CePdIn, the data suggest a smeared weak first-order superconducting
transition close to T. The normal state electronic specific
heat coefficient displays logarithmically divergent behavior, comparable to
CeCoIn and in agreement with 2D quantum criticality of spin-density-wave
type
Magnetization study on the field-induced quantum critical point in YbRh_2Si_2
We study the field-induced quantum critical point (QCP) in YbRhSi by
low-temperature magnetization, , and magnetic Gr\"uneisen ratio,
, measurements and compare the results with previous thermal
expansion, , and critical Gr\"uneisen ratio, , data
on YbRh(SiGe). In the latter case, a slightly
negative chemical pressure has been used to tune the system towards its
zero-field QCP. The magnetization derivative is far more singular than
thermal expansion, reflecting a strongly temperature dependent pressure
derivative of the field at constant entropy,
(: molar volume), which saturates at T/GPa for .
The line , previously observed in Hall- and thermodynamic
measurements, separates regimes in - phase space of stronger
) and weaker ) divergent .Comment: 4 Pages, 3 Figures, submitted to Proceedings of ICM 2009 (Karlsruhe
Multiple metamagnetic quantum criticality in SrRuO
Bilayer strontium ruthenate SrRuO displays pronounced non-Fermi
liquid behavior at magnetic fields around 8 T, applied perpendicular to the
ruthenate planes, which previously has been associated with an itinerant
metamagnetic quantum critical end point (QCEP). We focus on the magnetic
Gr\"uneisen parameter , which is the most direct probe to
characterize field-induced quantum criticality. We confirm quantum critical
scaling due to a putative two-dimensional QCEP near 7.845(5) T, which is masked
by two ordered phases A and B, identified previously by neutron scattering. In
addition we find evidence for a QCEP at 7.53(2) T and determine the quantum
critical regimes of both instabilities and the effect of their superposition
Ferromagnetic quantum critical fluctuations in YbRh_2(Si_{0.95}Ge_{0.05})_2
The bulk magnetic susceptibility of
YbRh(SiGe) has been investigated %by ac-and
dc-magnetometry at low temperatures and close to the field-induced quantum
critical point at T. For T a Curie-Weiss law with a
negative Weiss temperature is observed at temperatures below 0.3 K. Outside
this region, the susceptibility indicates ferromagnetic quantum critical
fluctuations: above 0.3 K, while at low temperatures
the Pauli susceptibility follows and scales with
the coefficient of the term in the electrical resistivity. The
Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the
critical field.Comment: Physical Review Letters, to be publishe
Divergence of the Magnetic Gr\"{u}neisen Ratio at the Field-Induced Quantum Critical Point in YbRhSi
The heavy fermion compound YbRhSi is studied by low-temperature
magnetization and specific-heat measurements at magnetic fields
close to the quantum critical point ( T, ). Upon
approaching the instability, is more singular than , leading to a
divergence of the magnetic Gr\"uneisen ratio .
Within the Fermi liquid regime, with
and T which is consistent with
scaling behavior of the specific-heat coefficient in
YbRh(SiGe). The field-dependence of indicates
an inflection point of the entropy as a function of magnetic field upon passing
the line previously observed in Hall- and thermodynamic
measurements.Comment: 4 pages, 3 Figure
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