| RECENT PROJECTS |
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| PIs: |
W. Pan (Sandia National Laboratory), D. Tsui |
| Funding: |
NSF and DOE |
| Personnel: |
W. Li, J. S. Xia, C. Vicente, N.S. Sullivan, L. N. Pfeiffer, K. W. West |
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Careful measurements down to very low temperatures (1 mK) of the quantum Hall plateau-to-plateau transition
have been carried out for long-range Columbic disordered two-dimensional electron systems embedded in
AlxGa1-xAs-Al0.32Ga0.68 As heterostructures with x=0 and 0.21%.
A cross-over behavior is observed form the high temperature (1.2k) non-universal scaling regime to a low
temperature, universal scaling regime, with the temperature exponent
k ranging from 0.58 to 0.42 respectively. The crossover temperature increases with increasing x
from 120 mK for x=0% to 250 mK for x=0.21%.
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Temperature dependence of the dRxy/dB for the transverse Hall resistance Rxy for?
applied magnetic fields B. k is the fitted exponent.
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| References |
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?Crossover from non-universal scaling regime to universal scaling regime in quantum Hall plateau
transition?,
W. Li, J. S. Xia, C. Vicente, N. S. Sullivan, W. Pan, D. C. Tsui, L. N. Pfeiffer and K. W. West,
Phys. Rev. B 81, 033305-033309 (2010).
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| PIs: |
D. Candela (University of Massachusetts), N. S. Sullivan (University of Florida) |
| Funding: |
CGRP and NSF |
| Personnel: |
Chao Huan, Sung Su Kim, Liang Yin, J. S. Xia |
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NMR studies have been carried out from 1.2 to 0.010 K of 3He impurities in solid 4He
for 3He concentrations ranging from 20 to 2000 ppm . Sharp changes in both the spin-spin relaxation
times (T2) and the signal amplitudes are observed at low temperatures (from ~0.08 to 0.2 K)
corresponding to phase separation with the formation of liquid nanodroplets of 3He at low
temperatures. A novel low noise preamplifier was developed that could operate at low temperatures and in high
magnetic fields and thus deployed near the NMR cell in order to observe the weak signals at very low concentrations.
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| References |
?NMR Studies of 3He Impurities in 4He in the Proposed Supersolid Phase?,
S. S. Kim, C. Huan, L. Yin, J. S. Xia, D. Candela and N. S. Sullivan,
J. Low Temp.
Phys. 158, 584-589 (2010).
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?A Novel Design of a Low Temperature Preamplifier for Pulsed NMR Experiments of Dilute 3He
in Solid 4He?,
C. Huan, S. S. Kim, L. Phelps, J. S. Xia, D. Candela and
N. S. Sullivan,
J. Low Temp.
Phys. 158, 692-696 (2010).
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| PI: |
F. Zapf (Los Alamos National Laboratory) |
| Funding: |
DOE |
| Personnel: |
L. Yin (UF-NHMFL), J.S. Xia (UF-NHMFL),
A. Padhuan-Filho (Instituto de
Fisica, Universidade de Sao-Paulo), N.S.
Sullivan (UF-NHMFL). |
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AC magnetic susceptibility measurements at very low temperatures (to 1 mK) of the
organic compound NiCl2-4SC(NH2)2 have been used to
determine the lower and upper critical fields, Hc1 and Hc2,
respectively, for the field- induced Bose-Einstein condensation. The transitions
were determined from measurements of the for temperatures down to 1 mK and for
fields from 1 to 13 T. The key parameter is the exponent for the temperature dependence
of Hc1 given by Hc1(T)-Hc1(0) =aT
which is predicted to be 3/2 for a 3D BEC condensation.
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Observed critical fields, Hc1 ~2 T and
Hc2 ~12 T determined from discontinuities
in field dependence of magnetization M(blue curve for
Ni S=1 spins in DTN a 3D XY anti-ferromagnet. |
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| References |
T. Giamarchi, C. Ruegg, and O. Tchernyshov, Nature Physics 4, 198 (2008).
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L. Yin, J. S. Xia, V. Zapf, N. S. Sullivan, A. Padhua-Filho, Phys. Rev. Lett, 101,
187205 (2008).
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?Magnetic Susceptibility Measurements at Ultra-low Temperatures?,
L. Yin, J. S. Xia, N. S. Sullivan, V. Zapf and A. Padhua-Filho,
J. Low Temp. Phys.
158, 710-715 (2010).
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| PI: |
Y. Lee |
| Funding: |
IHRP and NSF |
| Personnel: |
H.C. Choi, A.J. Gray, C. Vicente, and J-S. Xia |
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We investigate the influence of strong magnetic fields on superfluid 3He in high porosity
aerogel. As in the pure bulk, it is expected that strong magnetic fields will split the
superfluid transition into two transitions, namely the normal Fermi liquid to the superfluid
A1-phase and the A1-phase to the A2-phase. We will investigate the field dependence of the
A1-A2 splitting for the full pressure range and magnetic fields up to 15 Tesla.
The A1-phase is unique in nature since it is a fully spin polarized superfluid. The
existence of such a polarized superfluid is expected on the basis of particle-hole asymmetry
but has not yet been observed in the presence of strong quasiparticle scattering.
We propose to determine this splitting and its dependence on pressure. The measurements at
low pressures near the critical pressure have a potential to reveal astounding phenomena
related to the quantum phase transition. Since the splitting is expected to be smaller than
for bulk liquid (where it is ~60 mK/Tesla at melting pressure) and due to the low superfluid
transition temperatures (< 2mK), this project requires the ability to produce magnetic fields
larger than 10 Tesla with a nuclear demagnetization stage. The High B/T Facility, equipped
with a 15 Tesla superconducting magnet and a PrNi5 nuclear demagnetization stage is a
perfect platform and is the only place for this proposed research in this country.
Simultaneous measurements of high frequency shear impedance of the pure and dirty
superfluids will be performed. This research will provide important and urgent information
on the superfluid phases in aerogel and make a significant contribution in completing the
phase diagram of this system. Technically, the high frequency shear impedance measurement
will prove as a valuable tool to study quantum fluids in high magnetic fields since it does
not require field dependent tuning and is sensitive to all the transition features including
the first order A-B transition. This research also promotes the development of dielectric
constant thermometers for use at high magnetic fields and low temperatures.
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| References |
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?Acoustic Impedance Measurements of Superfluid 3He/Aerogel in High Magnetic Fields?,
C.L. Vicente, J-S Xia, H.C. Choy, A.J. Gray, Y. Lee, G. Gervais, W.P. Halperin, N. Moulders
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Presented at QFS2003
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| Flash Presentation (468kb)|
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| PI: |
D. Candela, W.J. Mullin (University of Massachusetts),
E.D. Adams and N.S. Sullivan (University of Florida) |
| Funding: |
IHRP and NSF |
| Personnel: |
H. Akimoto, J-S. Xia |
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An important effect predicted by Fermi-liquid theory is the field-induced relaxation of transverse spin currents.
Unlike all other transport coefficients, the transverse spin diffusion should tend to a finite limit at low
temperatures in high magnetic fields. The NMR spin echoes technique was used to measure the
transverse diffusion to test for the predicted field dependence in dilute 3He-4He
mixtures under extremely high B/T conditions, B = 14.75 T and T
≥ 1.73 mK. The 3He concentration x3
was adjusted close to 3.8% at which the spin-rotation parameter μM0
vanishes. In this way the transverse diffusion coefficient D┴ and
longitudinal spin coefficient D║ were measured
while keeping μM0 < 1. It is found that the temperature
dependence of D┴ deviates strongly from 1/T2, with
anisotropy temperature T = 4.26 mK. This value is close to the theoretical
prediction for dilute solution and suggests that spin current relaxation remains finite as
temperature tends to zero. This is the first practice of NMR at such low temperatures and
high magnetic fields.
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| Publications |
"New evidence for zero-temperature relaxation in a spin-polarized Fermi liquid",
H. Akimoto, D. Candela, J.S. Xia, W.J. Mullin, E.D. Adams and N.S. Sullivan, Phys. Rev. Lett. 90, 105301 (2003)
| Summary (HTML)
| Full Text (PDF 220 K)
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"Viscosity of Highly Polarized Very Dilute 3He-4He Mixtures",
H. Akimoto, J.S. Xia, E.D. Adams, D. Candela, W.J. Mullin and N.S. Sullivan, Int. J. Modern Phys. B16, 3117-3122 (2002)
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"Spin Transport in Very Dilute 3He-4He at Very High B/T",
H. Akimoto, J.S. Xia, E.D. Adams, D. Candela, W.J. Mullin and N.S. Sullivan, J. Low Temp. Phys. 126, 109-111 (2002)
| Summary (HTML)
| Full Text (PDF 4.56 M)
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"Non-Linear Dynamics of Dilute 3He in 4He at Very High B/T",
H. Akimoto, E.D. Adams, D. Candela, W.J. Mullin, V. Shvarts, N.S. Sullivan and J.S. Xia, Physica, B 284, 313 (2000)
| Summary (HTML)
| Full Text (PDF 162 K)
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