High B/T Facility: Breakout
• Neil Sullivan
• 2014 Users Committee Meeting
• Tallahassee, FL
• October 10-11, 2014
High B/T Facility
Unique High Field-Low Temperature Capabilities
 Provide Users access to high fields and ultra-low
temperatures, simultaneously
in an ultra-quiet environment
 Three stations for users
1990 Bay 2: B=8T, Tmin ~ 0.07 mK, homog. ~ 10-4 /cm
(open to NHMFL Users 2007)
1998 Bay 3: B=15/16.5T, Tmin ~ 0.4 mK,
homogeneity 1.6x10-5 /cm,
8 nW cooling power, t > 6 wks @ 1 mK
2004 Annex: 10 T/40 mK -- fast turnaround
test samples & cell design
 Capabilities
ultrasound, transport, heat capacity, NMR/NQR to 1100MHz,
magnetic susceptibility, resistivity, dielectric susceptibility
 Users work with staff for optimum design and automated data acq
Priorities, New Directions
1.
Reduce length of queue for magnet time
--- currently approx. 9 months
2.
Improve staff support
--- cell design and instrumentation
requires close work with local staff
3.
Expand parameter space
--- increase B > 16.5 T
Plan for HTS magnet (needs new location)
4. Advanced Low T instrumentation
--- exploit low physical temperature
HIGH B/T OPERATIONS
MICROKELVIN LAB. & WILLIAMSON ANNEX
< 2007: Bay 3 only
2007 --- added Bay 2 (part-time)
> 2015 plan to add HTS magnet
High B/T site
High B/T
700 m
Remote Site (New Physics Building)
High Bay Area
Need additional staff
and instrumentation
Physics
AMRIS
New Physics Building
3 ft
Top View Physics High Bay
HTS Magnet Example
2013-14 Facility Stats Overview
Facility Statistics
 18 users: 8 users on-site for experiment, 10 present only for set-up
6% of on site users were students or postdocs
94% were senior personnel
Research area all condensed matter physics
 834 magnet days available to users -- 95% to external users
 133% subscription rate
25% of proposals declined/deferred
Operation Mode
 1-2 user groups on-site each week
 Superconducting magnets run 24/7 for 35 weeks /year
set-up ~ 10 weeks per year
maintenance ~ 7 weeks per year
High B/T Facility
Growth: 2006-14
30
25
Typical experiment:
1 PI, 2.5 Co-PIs
1 local collaborator, 1 sample maker
1 sample characterization
0.5 postdoctoral fellow, 0.5 graduate student.
Fabrication of sample mount
Lasts 6-18 months (varies widely)
Uses 4000-6000 liters liq. He
Other
5%
Research Areas
Heavy
Ferm.
10%
Frust.
Mag.
BEC
37%
60
50
20
40
15
30
10
20
5
10
0
0
2006 2007 2008 2009 2010 2011 2012 2013 2014
Opened Bay 2
+ Annex
FQHE
33%
Qu.
FluidsSolids
15%
Helium costs ($1k)
Funding ($10k)
No. Users
Publications
Canada
7%
Origin PIs
China
28%
Europe…
US Nat.
Labs
20%
US Univ.
44%
High B/T User Science
Competing quantum Hall phases:
Second Landau Level of 2D Electron Systems
Quantum Hall Effect in Second Landau Level
Recent progress in fabrication of high-quality low-density samples
allows one to probe exotic quantum Hall states such as the
n =5/2 and 7/2 states a new regime where the electron-electron
interactions are strong.
New Low Temperature Results
First observation of anisotropic transport for n = 7/2 in a high-quality
dilute (n=5x1010 cm-2 ) 2D electron system.
New behavior attributed to a large Landau level mixing effect that
perturbs the pairing stability of composite limit.
upturn in the energy gap seen for n < 5x1010 cm-2,
spin unpolarized ground state
Competing quantum Hall phases in the second
Landau level in the low-density limit
W. Pan (Sandia), D. C. Tsui, K. W. Baldwin, K. W. West, L. N.
Pfeiffer (Princeton Univ.) A. Serafin, L. Yin, J. S. Xia ( Univ.
Florida)
Phys. Rev. B 89, 241302(R) (2014).
Science Driver:
Condensed Matter: FQHE: 2DES
High B/T User Science
Search for quantum Wigner solid and phase transition to
liquid state in a dilute 2D hole GaAs quantum well.
Liquid
H
rs
~ 37
Condensed Matter: 2D electron systems
H
FQ 1/3
=
=
1Q
Density p
Proposed phase diagram
Science Driver:
P
RI
Wigner Solid
Magnetic Field B
Results: observe an isotropic incipient
Wigner solid in the liquid state!
Ultra-low Temperature Transport studies of
Low Density Two-dimensional Hole System
Xuan Gao (Case Western Reserve University),
G. Boebinger, (NHMFL, Florida State University)
A. Serafin, J. S. Xia, Liang Yin (Univ. of Florida)
-- submitted to Nature
Support: NSF/DMR
Plots of magnetoresistivity at 4mK. Density p in units of 1010/cm2. The dash line
illustrates the evolution/melting of 2D Wigner solid while increasing the density p.
High B/T User Science
Bose Glass in
Doped Quantum Magnet
Ni(Cl1–xBrx)2·4SC(NH2)2
Novel equilibrium Bose fluid
realized for quantum organic magnets in high B
Disorder intro. in controlled manner (Br doping – stretch bond)
Results:
New state: Bose glass for 12<B<17.5T & T < 250mK
High precision susceptibility measurements (1.5 -15 mK)
allowed detection of critical exponents
Bose glass and Mott glass of quasiparticles in a
doped quantum magnet
T. Roscilde (Lyon), A. Padhuan-Filho (Sao Paulo), R. Yu (Univ. Houston),
S. Haas (Univ. So. Cal.) , A. Steppke (Max Planck Inst., Dresden), V. Zapf
(LANL), L. Yin et al. (Florida)
Nature 489,379 (2012)
Science Driver:
Condensed Matter: BEC/Bose glass
High B/T User Science
Quantum Spin Ice:
Pyrochlore Quantum Magnet Tb2Ti2O7
Science Driver:
Condensed Matter: frustrated magnetism
AC magnetic susceptibility measurements
new phases at low temperatures
I.
II.
Quantum spin ice, T<140 mK
Quantum kagome lattice
T< 50 mK, H: 0.08 – 0.7 T
Low-Temperature Low-Field Phases of the
Pyrochlore Quantum Magnet Tb2Ti2O7
Needed high sensitivity, low T susceptibility cell
Q. J. Li, X. F. Sun (Hefei National Lab., China),
L. Yin, J. S. Xia, Y. Takano et al. (Univ. of Florida)
Phys. Rev. Lett. 110, 137201 (2013).
New User Group
Supported by National Natural Science Foundation of China
High B/T Facility
Weaknesses
•
Long wait time in queue for magnet time after proposal acceptance
--- cannot respond rapidly for users competing in “hot” areas
•
Limited staff -- two supported by NHMFL, two by UF
--- insufficient to operate robust user facility
Competition
•
Rapid growth of High B/T at Laboratory for Extreme Conditions (China)
(considerable resources)
Also Inst. Solid State Physics, (Vienna Univ. of Technology)
•
Aging infrastructure (Tallahassee has helped in emergencies)
0.05 mK + 8T vector magnet
Strategic Goal: B> 30 T at sub-mK
Expand Parameter Space
Extend available B at ultra-low temperatures
to 30-32 T, would allow users to conduct
experiments currently not possible elsewhere
Examples of Need:
1. Determine critical behavior at BEC transitions
2. High-density high-quality fqHall samples
(resolve questions exotic Hall states (5/2, 7/2)
3. A transitions in superfluid 3He B> 15 T. Probes
underlying physics of pairing symmetries relevant to HTS
4. High-field phase diagram nuclear spin
ordering in solid 3He
Samulon et al.
(2010)
Ba3Mn2O8
need LT data
Nijmegen
(2014)
?
Remeijer et al.
(1998)
High B/T site
High B/T
700 m
Remote Site (New Physics Building)
High Bay Area
Need additional staff
and instrumentation
Physics
AMRIS
New Physics Building
Competition:
High Field/ Low Temperature Research Facilities
1. Key Laboratory for Extreme Conditions
(Chinese Academy of Science) Li Lu
Nuclear Demagnetization Stage: 0.5 mK in 11T
Electron temperatures
In 2DES
2. International Center for Quantum Materials
(Peking University) Xi Lin (Dan Tsui Laboratory)
Ultrahigh Vacuum, Ultra Low Temperature and High
Magnetic Field Scanning Probe Microscope Unisoku,
400mK with 9T/2T/2T vector magnets, in situ
cleavage/deposition
Outreach Activities:
Tours, Undergraduate Research, Local Schools
Research Experience for Undergraduates
Robert Cumby (Bowdoin College): Superregenerative Detectors for NQR detection, (Sullivan)
Mathew W. Calkins (University of Florida): Implementation
of a Differential Hall Element Magnetometer, (Meisel ).
Maxwell Leonard (Illinois Wesleyan University): Magnetism
of a Spin-1/2 Triangular-Lattice Heisenberg Antiferromagnet, (Takano)
Science Quest UF 2014
- rising 10th graders live on campus for
one week, perform science
experiments, attend lectures
Enhance Science Content
Knowledge for K-8 Teachers:
PROMiSE Program (2009-2011)
UFUTuRES Program (2012-2014)
(Hershfield and Meisel)