arXiv 06/10/09

Title: M\"{o}bius Graphene Strip as Topological Insulator
( http://arxiv.org/abs/0906.1634 , 970kb) -- may be unrealistic experimentally at moment but very interesting

Title: Fabrication of the iron-based superconducting wire using Fe(Se, Te) ( http://arxiv.org/abs/0906.1636 , 394kb)

Title: AC transport in carbon-based devices: challenges and perspectives
( http://arxiv.org/abs/0906.1664 , 1116kb)

Title: How the SiC substrate impacts graphene atomic and electronic structures
\\ ( http://arxiv.org/abs/0906.1701 , 296kb)

Title: Destruction of graphene by metal adatoms
\\ ( http://arxiv.org/abs/0904.0807 , 378kb)

NDNC 2009 Tuesday

2nd day at NDNC conference (http://www.mrs.org/s_mrs/sec.asp?CID=19286&DID=241928)
besides Isaac's poster and my talk, Ruoff gave an overview talk of their graphene work over the years. Interesting isotopically dependent study (use C-13 deposited graphene etc), a technique also used by them in 2008 for graphite oxide.
[Interesting idea of possible enhancement of thermal conductivy in isotopically pure graphene, something Cardonna also mentioned when he visited us in Purdue]
They have a company grapheneenergy.net

Calizo (Baladin student) talked about UV light (325nm) Raman on graphene --- 2D band very much suppressed ---- would the opposite be true, ie if using IR or MIR light would 2D be enhanced??

Mott insulator at contacts

On the drive to Denver from Aspen, my wife (nonphysicist) asked me to explain Mott insulator --- and she questions the standard explanation of insulating state caused by strong (on-site) repulsive interaction -- how could it work if the Mott insulator is allowed to have contact with electrodes, if and one electron at one end of the Mott insulator is pulled (by e-field) away through the contact, creating a vacancy for the next electron to hop, and so on and won't be insulating. I found I can't explain this well and I don't really understand Mott insulator! Need to think more about it...

Aspen Friday

Morning: Mukund Vengalattore (UC Berkeley now Cornell) talked about spinor BEC --- very rich physics in presence of dipolar interaction (comparable with spinor interaction -- usually competing interactions give rich phases), use phase contrast imaging (similar to those used by Shin et al in Ketterle group to image spin imbalanced fermions), he showed impressive data on evolution of magnetic excitations, real time imaging of Lamor precessing etc -- even phases with both broken translation symmetry 'checker board' pattern and long range coherence -- kind of "supersolid"?

Smitha Vishvanath (UIUC) discussed possible interesting physics arise from superfluid regions coupled via insulator regions;

Han Pu (Rice) talked about interesting physics in dipolar fermions (eg KRb molecules), suggested such phases as deformed fermi surface
[constant deformation as variational parameter--- what about space-dependent deformation would that lower energy further?]
Interesting work on dipolar BEC: Meystre: PRA 75, 053604 (2007) and JL Bohn PRA 74 013623 (2006), Laser Physics 19, 547(2009)

Aspen Thursday

Morning:
attended Josh Davis and Eskos's session on string theory and QHE, Eskos work on QC conductivity in QH transition calculated by AdS/CFT very interesting, comapred to earlier CMP work:
Damle & Sachdev PRB 1997
Chen, Fisher and Wu 1993
Basically predicts "universal" shape of sigma(omega) as a function of omega/T, with a peak in the function.
string theory methods seem to give answers quicker and nicer.
I pointed out to Eskos that the peak of omega/T still need to be determined to guide experiments.
Also asked any sum rule (oscillation strengths for the function).
Semenoff pointed out that such phenomena should be best observed in graphene, esp. N=0 LL --- measure AC conductivity there!
Later called Zhigang on this and he will look into the data. So far IR spectroscopy he did not easy to extract pure AC conductivity, but possible.

Afternoon: Cheng-chin held an informal discussions on 2D BEC. Earlier Jason Ho, Cheng and I had this interesting discussions in our office --- Hall mark of 2D KT transition in superfluids is the jump of SF density at KT transition (predicted by Nelson et al, measured by John Reppy PRL) , would be nice if such (staitc SF density) jump can be observed directly in atoms, but audience suggested this would be almost round off in a finite system like trap.
Jason emphasized that holy grail: how to measure superfluid properties (esp. SF density) in cold atom clouds!! (also eg second sound...)
Cheng has loaded pancake BEC and some data on quasi-2D behavior.

This week's colloquium is by Daniel Bauman from Harvard on first 10^-10 seconds of universe,
cool points:
1) data so far suggest universe very flat, trivial topology; data also seen on "acausal correlation in density fluctuations in present universe" --- related to inflation that expands quantum fluctuations into density fluctuations beyond horizon
2) polarization CMB images can probe gravitation waves as only 400K years after bing Bang, much easier to probe than LIGO (gravitational waves at present), may prove inflational theory!
3) not addressing the 10^120 (ie where the cosmological constant is from) issue though

arXiv 06/03-04/09

Title: Electronic Radio-Frequency Refrigerator ( http://arxiv.org/abs/0906.0597 , 473kb)

Title: Evidence for Graphene Edges Beyond Zigzag and Armchair ( http://arxiv.org/abs/0906.0688 , 1860kb)

Title: More is the Same; Phase Transitions and Mean Field Theories
( http://arxiv.org/abs/0906.0653 , 329kb) --- a very illuminating article by a master, helpful to understand many contexts

Title: Threshold of a Random Laser with Cold Atom
Journal-ref: Physical Review Letters 102 (2009) 173903\\ ( http://arxiv.org/abs/0812.0266 , 495kb)


arXiv:0906.0771
Title: Exotic plasmon modes of double layer graphene

Title: Relaxation of compressive strain in epitaxial graphene through wrinkle
formation \\ ( http://arxiv.org/abs/0906.0896 , 1078kb) -- relevant for our CVD graphene

Title: Resistivity of Graphene Nanoribbon Interconnects ( http://arxiv.org/abs/0906.0924 , 204kb)

Title: Electron-electron interactions and doping dependence of the two-phonon
Raman intensity in graphene \\ ( http://arxiv.org/abs/0906.0975 , 57kb)

Aspen Wednesday

Morning:
*Randy Hulet talked about recent data on very strongly interacting Li-7 BEC (near Feshbach resonance) --- extremely interesting: as the BEC approaches resonance (stronger interaction), the chemical potential (measured from size of condensate) deviates from the value expected for BEC (even with beyond mean field Lee-Yang-Huang correction) and seems approaching the fermi energy as if the strongly interacting bosons starting to behave like fermions!
More data is needed to confirm this remarkable preliminary observation but much discussions followed in the workshop.
Some of such physics has been predicted in the paper by Fei Zhou:
http://arxiv.org/PS_cache/arxiv/pdf/0902/0902.0366v2.pdf
[Note added: Since the 3-body recombination loss is quite large when approaching the resonance, I think it might have something to do with the recent work on "loss/dissipation induced (dynamically generated) effective correlation/interaction", as discussed in Zoller et al: PRL 102, 040402 (2009) in relation to an experiment by Rempe et al: N. Syassen et al., Science 320, 1329 (2008) , in addition, Zoller has another visionary paper on strongly driven quantum systems :Nature Physics 4, 878-883 (2008) --- there could be a new paradigm of generating novel quantum phases "dynamically".
* Robin Cote gave a tutorial on AMO physics. I attended the part 2-3 on atoms and molecules.
interesting stuff mentioned:
- Peter Zoller's talk in NSF QIS workshop 2009: http://www.eas.caltech.edu/qis2009/program.html (many good talks)
- Rempe's work on using pulsed laser as repump? -- I can't find it though
- sympathetic coolding b/t molecules and alkali atoms (Heather Lewandowski)
- 2008 PRA's by E. Kuznetsova et al on polar molecule phase gates ("Analysis of experimental feasibility of polar-molecule-based phase gates") and STIRAP (Formation of deeply bound molecules via chainwise adiabatic passage)

During coffee break, had some extremely interesting discussions with Gordon Semenoff on graphene:
1) chiral symmetry breaking (Nambu mechanism) should be possible in graphene if can control Coulomb interaction (relative to hopping say) ---- in other words this corresponds to Mott transition as U/t increases, GS says electrons in graphene are not far from such transition, can probe say
1a) reducing t by stretching
1b) chemically modifying t (hopping) both very interesting experiments!
[Note--- the threshold U/t (~5, in real graphene value ~4) for fermions in honeycomb lattice not known -- Klauss Ziegler said he may be able to calculate, will follow up!]
2) chiral/sublattice polarization may occur in low B, and detectable with "sublattice valve"? (bilayer region etc. )
3) renormalization of speed of light and dependence on size --- later discussed with Dan Sheehy

Afternoon:
Had an interesting discussion with Dan Sheehy (LSU) --- 1) The "effective speed of light" (ie fermi velocity) in graphene in fact suppose to have higher order QED corrections, eg. proportional to ln(L/a), L sample size and a lattice constant, the velocity should approach c in vacuum for infinite sample. So finite-size (up to very large sample) dependent study may reveal such evolution --- good to measure v_F for a series of samples of different sizes! Finite freq, magnetic field variation and large density variation may also help. Check on various measurements of v_F in literature, eg. transport, optics, STM, Yacoby (n-dependent), and heat capacity? (not yet) -- they do not all agree! 2) BEC-BCS crossover of fermions on honeycomb lattice --- suppose to have no BCS SF because no fermi surface in honeycomb --? 3) discussed possible BCS BEC crossover in quantum Hall bilayer, if so, where is the cross over point in d/a (1.8?) --- need a bound state to appear? May check 2D bound state of a free hole to electron(s) from another layer?

arXiv 06/02/09

Title: Highly enhanced thermopower in two-dimensional electron systems at
milliKelvin temperatures
Authors: Srijit Goswami, Christoph Siegert, Matthias Baenninger, Arindam Ghosh,
Michael Pepper, Ian Farrer, David A. Ritchie
We report experimental observation of an unexpectedly large thermopower in
mesoscopic two-dimensional (2D) electron systems on GaAs/AlGaAs
heterostructures at sub-Kelvin temperatures and zero magnetic field. Unlike
conventional non-magnetic high-mobility 2D systems, the thermopower in our
devices increases with decreasing temperature below 0.3 K, reaching values in
excess of 100 $\mu$V/K, thus exceeding the free electron estimate by more than
two orders of magnitude. With support from a parallel independent study of the
local density of states, we suggest such a phenomenon to be linked to intrinsic
localized states and many-body spin correlations in the system.
\\ ( http://arxiv.org/abs/0906.0445 , 1132kb) --- interesting thermopower device involving QPC

Disordered graphene

Had very interesting discussion with Klauss on disrdered graphene today.

1) It is very interesting to monitor minimum conductivity (at Dirac point) to see how it evolves with disorder (eg exposure to plasma or hygrogenation). The prediction is very different for bilayer vs single layer graphene.

2) also it's interesting to look at WL (which we have been doing) and see how that differs for BLG vs SLG.

Website for the cold atom workshop at Aspen

http://people.ccmr.cornell.edu/~emueller/aspen/Quantum_Simulation/Overview.html

Aspen Tuesday

Morning: Marvin Girardeau (http://www.optics.arizona.edu/girardeau/ , amazingly still so active at such age) gave a chalk talk on his recent work on 1D fermi gas ---- apparently for attractive 1D fermi gas he can map it into 1D bose gas and solve exactly -- interestly consequence include eg., if confinement induced scattering length is negative, it may collapse.
Other topics discussed include p-wave FR of one/two? species fermions and its stability in 1D vs 3D.
[need to know more]

Interesting arXiv papers 06/01/2009

Title: Field-induced Kosterlitz-Thouless transition in the N=0 Landau level of
graphene
Authors: Kentaro Nomura, Shinsei Ryu, Dung-Hai Lee\\
At the charge neutral point, graphene exhibits a very unusual high resistance
metallic state and a transition to a complete insulating phase in a strong
magnetic field. We propose that the current carrier in this state are the
charged vortices of the XY valley pseudospin order-parameter. We study
energetics and the stability of this phase in the presence of disorder.
\\ ( http://arxiv.org/abs/0906.0159 , 329kb) --- relevant for Liyuan's experiment and QHE at N=0 (still unresolved)

arXiv:0906.0188
Title: Transport properties of graphene in the high-current limit


Title: Long-Range Interaction Between Adatoms in Graphene
Authors: Andrei Shytov, Dmitry Abanin, Leonid Levitov
\\ ( http://arxiv.org/abs/0812.4970 , 27kb)

LiRb stuff with Robin Cote

To discuss:
1) what important unknown questions on Li-Rb system, given what have been known:
2) states and preferred PA pathways and PR rates

Refs:
1) http://adsabs.harvard.edu/abs/2009PhRvA..79a2717M [Li7-Rb87 FR]
2) http://adsabs.harvard.edu/abs/2008arXiv0807.0417L [Madison analysis]
3) http://adsabs.harvard.edu/abs/2007arXiv0709.4554D [Li-6 Rb-87 FR]

http://meetings.aps.org/Meeting/DAMOP08/Event/84487

People to watch/chat with in Aspen -pt 1

Frequent discussions:
Robin Cote -- LiRb
Ziegler --- disordered graphene, WL, AC transport, quantum optics
Chin --- optical trapping
[SM2] Han Pu --- dipole interaction

[BE1 office] Allan Adams (MIT): string in condensed matter

ST 7 Veronica Ahufinger: disordered quantum gas

SM 23 Grigory E. Astrakharchik: 2D BEC! (http://arxiv.org/abs/0812.3844, http://arxiv.org/abs/0806.0039, http://arxiv.org/abs/0706.2855 --crystal of fermions)

Lincoln Carr (cold molecules http://arxiv.org/abs/0904.3175, also graphene: Phys. Rev. Lett. v. 100, p. 175503)

Ignacio Cirac (dissipation induced Pfaffian -- http://arxiv.org/abs/0905.1247, Non-abelian: http://arxiv.org/abs/0802.3163)

[SM 27] Veselin Filev (chiral magnetic physics connected to graphene? ...
http://arxiv.org/abs/0903.5345, http://arxiv.org/abs/0706.3811)

Thomas Gasenzer (out of equilibrium: http://www.springerlink.com/content/n7712uv90p84q713/

Victor Gurarie (out of equilibrium: http://arxiv.org/abs/0905.4498)

SM20 Werner Krauth (2D BEC: http://arxiv.org/abs/0710.5060)

Ganapathy Murthy (QHE)

Anatoli Polkovnikov (BEC)

Lode Pollet (disorder SF)

[SM] Gordon W. Semenoff (graphene QCD: http://arxiv.org/abs/0712.2439)

Daniel Sheehy (graphene Coulomb: http://arxiv.org/abs/0707.2945)

Simon Trebst (Microsoft station Q -- topological QC)

Masahito Ueda ("weak" dipole)

Monday in Aspen Center for Physics

ACP (http://www.aspenphys.org/) is basically a summer camp for physicists (most profs) from all fields of physics.

This morning I attended a talk by David Weiss (PSU) on designing neutral atom quantum computer and by Cheng Chin (Chicago) on his progress in Li-Cs mixed species quantum computer.

Cheng Chin has used interesting nanofabricated diffraction plate to create very stable triangular optical lattices
[look for paper by Klinger et al to come?]

Lunch: Robin Cote (UConn) mentioned calculation on LiRb systems: molecular potentials (by QChem codes) and photoassociation rates ... calc. fit with measured feshbach res. b/t (6Li, 87Rb) and (7Li, 87Rb).
[will followup with him]

Talked to Peter Reynolds, program manager from ARO, who shared an interest with holographic physics and topological insulator (3D), as connected to the string talk next.

Afternoon: I attended a colloquium by Clifford Johnson (USC) on string theory (AdS/CFT) with possible applications to condensed matter physics. Met two interesting guys, Josh Davis (http://arxiv.org/abs/0809.1876) and Esko Keski-Vakkuri (http://arxiv.org/abs/0905.4538, http://arxiv.org/abs/0805.4643) --- they have used AdS/CFT (effective to treat finite temperature systems) to calculate quantum Hall physics, esp. AC conductivity at finite T (http://arxiv.org/abs/0905.4538)！
[Questions for them -- how does this work for massless Dirac fermions in graphene? and other difficult finite-T problem., eg. 2D superfluid/superconductor. Can AdS/CFT treat disorder? ]

The speaker Clifford Johnson has mentioned interesting aspect about the "ideal fluid" aspect measured both in RHIC (hydrodynamics of strongly interacting quark gluon plasma) and in John Thomas group at Duke (cold Li fermions) where viscosity/entropy is low at 1/(4pi)...

Also in the afternoon Nikolai Prokofiev (UMass) proved a general theorem on disorder-driven phase transitions must go through inter-mixed phases (droplets) and claim there should be no such Superfluid-Mott transition
[Hmm need to learn more].

Stopped briefly on a chalk talk by Djordje Minic (Virginia Tech) on the physics of Rieman hypothesis in number theory and how it may be related to string theory?? (http://arxiv.org/abs/0903.4321 --- aha, I know the author back in old days!)

I am sharing an office with Cheng Chin and Klaus Ziegler (CM theorist from Ausburg who works on both graphene and cold atoms). Had an interesting discussion with Klaus on special plasmon modes and optical properties of graphene. He has several PRLs that I want to discuss with in coming days.

On way home met Biao Wu from CAS, former student of Qian Niu from Austin. He suggested several interesting experiments for 2D BEC: 1) quantum corral and quantum chaos with BEC reflecting from optical "billiard wall" (a sheet of blue detuned light) -- http://arxiv.org/abs/0812.4602, motivated by Hari Manoharan's famous STM quantum corral, but quantum chaos has not been experimentally observed; 2) use patterned (maybe lithography fabricated) Fibonacci or quasiperiodic potential to look at how BEC propagates in such potentials.