Wednesday, August 15, 2007

Kazushi Kanoda, Spin liquid behavior in organic charge transfer salts


Kazushi presented his results for spin liquid behavior observed in a member of the two dimensional charge transfer salt family κ-(ET)2X with counter ion X=Cu2(CN)3.

ET-molecules form a two dimensional pattern where two molecules form dimers and dimers form an anisotropic triangular lattice. The counter ions take one electron out of a dimer, leading to a half filled band. Kazushi stressed that in the organics, different ground states can be stabilized via changing the counter ions and tuning the pressure.

In distinction to the ambient pressure Mott insulator κ-(ET)2X with X=Cu2[N(CN)2]Cl,which undergoes antiferromagnetic long range order below 27K, the triangular lattice of the X=Cu2(CN)3 compound is almost isotropic. The key observation from NMR, µ-SR and susceptibility measurements is the absence of magnetic long range order down to 20mK (much smaller than the estimated size of the exchange interaction J~250K).

In the discussion it was pointed out that the Heisenberg model on a triangular lattice has an ordered ground state, but that a disordered ground state can be stabilized by ring exchange terms that are expected to be important close to a Mott transition. Indeed the material undergoes a pressure induced Mott transition from insulator to metal at p=0.3-0.4GPa.

Next to the existence of a Mott insulator without broken symmetry, the most spectacular observation of Kanoda and collaborators is the fact that the low T behavior of the system seems gapless. The heat capacity vanishes linearly with T and the susceptibility is finite. This is consistent with the observation that the entropy of the spin liquid is larger that the entropy of the pressure induced superconductor as deduced from the Clausius-Clapeiron relation.

While there seem to be no long range order at low T, 13C-NMR, thermal conductivity and heat capacity measurements show indications for the onset of some inhomogeneous state below T=5K. Also, the spin lattice relaxation rate decreases with T3/2 below T=5K (it decreases as T1/2 at higher T). A broadening of the 13C-NMR lines and stretched exponential relaxation is the key argument supporting a magnetic field induced inhomogeneous state.

Open problems in this context are:

-is the gapless nature of the ground state related to the anomaly at 5K and the onset on inhomogeneities?

-what is the nature of the superconducting state? Is it different from other organics? (In this context Kazushi mentioned that the Knight shift in the superconducting state does not seem to vanish)

-Why is the charge response of this system rather different from other organics?

Buttom line: This material seems the first gapless spin-liquid in a quasi two dimensional Mott insulator. Upon pressure it becomes a superconductor. So far no theory was able to account for the rich behavior of this system. It is clearly a very sharply defined outstanding challenge!

Relevant papers:

Y. Shimizu, K. Miyagawa, K. Kanoda, M. Maesato, and G. Saito, 1H NMR and static susceptibility measurements have been performed in an organic Mott insulator with a nearly isotropic triangular lattice, κ-(BEDT-TTF)2Cu2(CN)3, which is a model system of frustrated quantum spins. The static susceptibility is described by the spin S=1/2 antiferromagnetic triangular-lattice Heisenberg model with the exchange constant J∼250  K. Regardless of the large magnetic interactions, the 1H NMR spectra show no indication of long-range magnetic ordering down to 32 mK, which is 4 orders of magnitude smaller than J. These results suggest that a quantum spin liquid state is realized in the close proximity of the superconducting state appearing under pressure.Phys. Rev. Lett. 91, 107001 (2003)

Y. Kurosaki, Y. Shimizu, K. Miyagawa, K. Kanoda, and G. Saito, Phys. Rev. Lett. 95, 177001 (2005)

14 comments:

Carlos said...

These articles are fantastic; the information you show us is interesting for everybody and is really good written. It’s just great!! Do you want to know something more? Read it...:Great investment opportunity in Costa Rica: jcondos house, costa rica beach condos, condos rentals. Visit us for more info at: http://www.jaco-bay.com/

Anonymous said...

Hello !.
You re, I guess , probably curious to know how one can collect a huge starting capital .
There is no need to invest much at first. You may start to get income with as small sum of money as 20-100 dollars.

AimTrust is what you haven`t ever dreamt of such a chance to become rich
The firm represents an offshore structure with advanced asset management technologies in production and delivery of pipes for oil and gas.

It is based in Panama with affiliates everywhere: In USA, Canada, Cyprus.
Do you want to become really rich in short time?
That`s your choice That`s what you desire!

I feel good, I began to get income with the help of this company,
and I invite you to do the same. It`s all about how to choose a correct companion who uses your funds in a right way - that`s the AimTrust!.
I take now up to 2G every day, and my first deposit was 1 grand only!
It`s easy to start , just click this link http://zyjibogyku.s-enterprize.com/atutyf.html
and lucky you`re! Let`s take this option together to get rid of nastiness of the life

Anonymous said...

Good day, sun shines!
There have been times of hardship when I didn't know about opportunities of getting high yields on investments. I was a dump and downright stupid person.
I have never thought that there weren't any need in big initial investment.
Now, I feel good, I started to get real money.
It's all about how to choose a correct companion who utilizes your funds in a right way - that is incorporate it in real deals, and shares the income with me.

You can get interested, if there are such firms? I'm obliged to answer the truth, YES, there are. Please get to know about one of them:
http://theinvestblog.com [url=http://theinvestblog.com]Online Investment Blog[/url]

Anonymous said...

A friend of mine mentioned 2012 last night to me and it's the first I heard about it so I jumped on here out of curiosity. I think it's kind of sick and sounds like a bunch of skeptical jargon.
I choose to live every day like it is the last because let's be real, WHO THE HELL KNOWS what is going to happen or when it's your time to go on. The past is history, the future is a mystery and now is a gift, thats why it's called the present. It's not healthy to sit around and trip out about when you will die. Stop wasting your time you have now.
[url=http://2012earth.net/mayan_calendar_2012.html
]switch to consciousness 2012
[/url] - some truth about 2012

Anonymous said...

A friend of mine mentioned 2012 last night to me and it's the first I heard about it so I jumped on here out of curiosity. I think it's kind of sick and sounds like a bunch of skeptical jargon.
I choose to live every day like it is the last because let's be real, WHO THE HELL KNOWS what is going to happen or when it's your time to go on. The past is history, the future is a mystery and now is a gift, thats why it's called the present. It's not healthy to sit around and trip out about when you will die. Stop wasting your time you have now.
[url=http://2012earth.net
]2012 end of world
[/url] - some truth about 2012

Anonymous said...

Glad to greet you, ladies and gentlemen!

Let me introduce myself,
friends call me Peter.
Generally I’m a social gmabler. recently I take a great interest in online-casino and poker.
Not long time ago I started my own blog, where I describe my virtual adventures.
Probably, it will be interesting for you to find out my particular opinion on famous gambling projects.
Please visit my diary. http://allbestcasino.com I’ll be interested on your opinion..

free same sex stories said...

When it was clear that the squids were ontheir way, he called the Pretty Boys. Bessie wont be doin you boys any time soon.
family porn stories
sex stories women taboo
free adult bondage pictures stories
nifty erotixc stories
gay daddy sex stories
When it was clear that the squids were ontheir way, he called the Pretty Boys. Bessie wont be doin you boys any time soon.

Anonymous said...

I love novelsc.blogspot.com! Here I always find a lot of helpful information for myself. Thanks you for your work.
Webmaster of http://loveepicentre.com and http://movieszone.eu
Best regards

Invertir en oro said...

Thanks for sharing this info because is very good and i like to post like this.

Cialis kaufen said...

Interesting. Heard some completely new facts.

www.rivas-vaciamadrid.biz said...

The dude is completely just, and there is no suspicion.

Ideas de negocios said...

Thanks for taking the time to discuss this, but I am firmly convinced of this and love to learn more about the subject. If possible, acquire knowledge, would you update your blog with more information? It is very helpful to me

Free Poker said...

The beauty of this Novel Aspects of Superconductivity website online is amazed. I like your blog.
--------------------------
Link to my site: No Deposit Poker Bonuses for Poker rooms.

Leigh said...

There is so much more we have to learn about the properties of superconductors.