Patent Application
20170261831
Superconductivity has stimulated much interest over the past century due to its technological importance. The loss of electrical resistance depends on temperature and the critical temperature Tc at which superconductivity appears has gradually increased over time since it was first discovered by Heike Kamerlingh Onnes 1911. The discovery of high-Tc materials (with Tc>90° K) in 1986 in ceramic materials was a major milestone since it is possible to operate at liquid nitrogen temperature. The ultimate aim are superconductors that work at room temperature since it would save enormous amount of energy because electrical resistance is the source of huge losses during transport and distribution of electric energy. Therefore, there is a strong demand for significantly improving the Tc, in order to be able to fully exploit the potential use of such materials in the concerned technological fields and technical applications.
Description of the Related Application
In conventional superconductors, the current is carried by bound pairs of electron known as Cooper pairs. According to BSC theory, phonon mediate the pairing and Tc is given by:
T
c
∞ωe
−1/gN(E
) (1)
where w is the phonon cut-off frequency of the phonons mediating the electron coupling, g is the electron-phonon coupling strength and N(EF) is the density of states per unit energy at the Fermi level (T. W. Ebbesen, J. S. Tsai, K. Tanigaki, J. Tabuchi, Y. Shimakawa, Y. Kubo, I. Hirosawa and J. Mizuki “Isotope Effect on Superconductivity in Rb3C60” Nature, 355, 620 622 (1992)). The Tc dependence on the phonon is complex but it has been observed that bond-softening can lead to an increase in the critical temperature as reported for instance in the case MgB2 (A. V. Pogrebnyakov, J. M. Redwing, S. Raghavan, V. Vaithyanathan, D. G. Schlom, S. Y. Xu, Qi Li, D. A. Tenne, A. Soukiassian, X. X. Xi, M. D. Johannes, D. Kasinathan, W. E. Pickett, J. S. Wu and J. C. H. Spence “Enhancement of the superconducting transition temperature of MgB2 by a strain-induced bond-stretching mode softening” Phys. Rev. Lett. 93, 147006 (2004)).
On the other hand, it is known that light and matter can enter into the strong coupling regime by exchanging photons faster than any competing dissipation processes. This can be achieved by placing the material in a confined electromagnetic environment, such as a Fabry-Perot (FP) cavity composed of two parallel mirrors that is resonant with a transition in the material. Strong coupling leads to the formation of two polaritonic states separated by the so-called Rabi splitting ωR. According to quantum electrodynamics, in the absence of dissipation, the Rabi splitting is given by:
where ω is the cavity resonance or transition energy, ∈0 the vacuum permittivity, v the mode volume, d the transition dipole moment of the material and nph the number of photons present in the system. The last term implies that even in the dark, the Rabi splitting
ΩR has a finite value which is due to the interaction with the vacuum electromagnetic field.
As background state of the art, one can refer to the following documents: Haroche, S. “Cavity quantum electrodynamics” in: J. Dalibard, J. M. Raimond, J. Zinn-Justin (Eds.), Fundamental Systems in Quantum Optics, Les Houches Summer School. Session LIII, North Holland, Amsterdam. 1992/Schwartz, T., Hutchison, J. A., Genet, C. & Ebbesen, T. W. “Reversible switching of ultra-strong coupling” Phys. Rev Lett. 106, 196405 (2011)/Kéna-Cohen, S., Maier, S. A. & Bradley, D. D. C. “Ultrastrongly coupled exciton-polaritons in metal-clad organic semiconductor microcavities” Adv. Opt. Mater. 1, 827-833 (2013)/Hutchison, J. A., Schwartz, T., Genet, C., Devaux, E. & Ebbesen, T. W. “Modifying chemical landscapes by coupling to the vacuum fields” Angew. Chem., Int. Ed. 51, 1592-1596 (2012)/Hutchison, J. A., Liscio, A., Schwartz, T., Canaguier-Durand, A., Genet, C., Palermo, V., Samori, P. & Ebbesen, T. W. “Tuning the work-function via strong coupling” Adv. Mater. 25, 2481-2485 (2013)/A. Shalabney, J. George, J. A. Hutchison, G. Pupillo, C. Genet and T. W. Ebbesen “Coherent coupling of molecular resonators with a microcavity mode” Nature Commun. 6: 5981 (2015)/A. Shalabney, J. George, H. Hiura, J. A. Hutchison, C. Genet, P. Hellwig, T. W. Ebbesen “Enhanced Raman scattering from vibro-polariton hybrid states” Angewandte Chemie Int. Ed. 54, 7971-7975 (2015)/E. Orgiu, J. George, J. A. Hutchison, E. Devaux, J. F. Dayen, B. Doudin, F. Stellacci, C. Genet, J. Schachenmayer, C. Genes, G. Pupillo, P. Samori and T. W. Ebbesen “Conductivity in organic semiconductors hybridized with the vacuum field” Nature Materials 14, 1123-1129 (2015).
From WO 2013/017961, it is known to make use of strong coupling in order to modify the work function of materials (i.e. the energy required to extract an electron from the material) and the rate of chemical reactions.
From WO 2015/008159, it is known to make use of strong coupling in order to modify the electrical properties of an organic or molecular material.
Now, the inventors have found, in an unexpected and surprising manner, that the superconductivity of materials can be influenced by strongly coupling said materials to the vacuum field. The Tc of the superconductors is increased by strongly coupling the phonon of the material to an optical mode in the infrared as illustrated in
ωR.
Thus, the main object of the present invention is a method to modify the superconductivity properties of a potentially or effectively superconductive material comprising the steps of providing a reflective or photonic structure and of placing said material in or on said structure, method characterized in that it consists further in providing a structure which has an electromagnetic mode which is by design, or can be made by way of adjustment or tuning, resonant with a transition in said superconducting material and in controlling, in particular enhancing, the superconductivity, and thus the mobility of the charge carriers, resulting in an increased electrical current, in said inorganic or molecular material, by means of strongly coupling said material to the local electromagnetic vacuum field and exploiting the formation of delocalized hybrid states.
The method according to the invention may also comprise or show one or several of the following secondary features or alternatives:
According to an advantageous embodiment of the invention, the method consists more precisely, by means of coupling to local electromagnetic vacuum field and exploiting the resulting rearrangement of the energy levels of the material, in inducing the formation of hybrid light-matter states in the material in order to increase its superconductivity said hybrid states extending over the mode volume of the electromagnetic mode.
In practice, the previously described method can be applied in a functional device comprising said reflective or photonic structure, said device being one of an electric device, an electronic device, an electro-optical device, an optoelectronic device, the superconductivity of which are significantly increased as a result of said method.
The invention also encompasses an electric, an electronic, electro-optical or optoelectronic device, comprising a superconductive material located in or on a reflective or photonic structure,
device characterized in that said structure has an electromagnetic mode which is by design or can be made by way of adjustment or tuning, resonant with a transition in said superconductive material and in controlling, in particular enhancing, the superconductivity and therefore the mobility of the charge carriers, and thus increasing the electrical current, in said superconductive material, by means of strongly coupling said material to the local electromagnetic vacuum field and exploiting the formation of extended macroscopic states in said material, namely states of spatial extension corresponding to the mode volume of the electromagnetic resonance.
Preferably, said device incorporates or makes use of one or several of the previously mentioned secondary features.
Advantageously, the reflective or photonic structure consists of an optical microcavity, preferably a Fabry-Perot cavity, the electromagnetic mode being a cavity mode.
More precisely, the structure may comprise two metallic or dielectric mirrors forming with the superconductive material a sandwich structure, the distance between said mirrors being adjusted to resonate with a phonon or vibration transition of said material, said opposite mirrors being arranged preferably transversally or longitudinally to the direction of displacement of the charge carriers.
Furthermore, the invention also comprises a machine or apparatus able and intended to perform at least one electronic, electro-optic, optoelectronic or optic function, wherein said machine or apparatus comprises at least one device as mentioned before, said device being designed to perform the method set out previously.
In terms of practical embodiments, one can notably refer to and rely on the teachings of the aforementioned PCT publications, namely WO 2013/017961 and WO 2015/008159, which are incorporated in the present specification by reference.
More specifically, the teachings related to the constructions shown in FIGS. 3A and 3B and in FIG. 8 of WO 2015/008159, and the associated description, can be used to put into practice the present invention.
Thus, a device according to the present invention can be realized by replacing the material 2 in FIGS. 3A and 3B or in FIG. 8 of WO 2015/008159 (or US 2016/154258) by a supraconductor material 2 having at least one phonon mode which can be coupled, such as for example C60 Rb3 or the family of materials related to C60 Rb2 Cs.
Finally, the invention also encompasses a method, a device and a machine or an apparatus as mentioned in any of the attached claims 1 to 16, and as illustrated schematically by way of two non limitative examples of embodiments in the attached
| Number | Date | Country | |
|---|---|---|---|
| 62307660 | Mar 2016 | US |
