diff options
author | Prefetch | 2021-12-01 19:38:28 +0100 |
---|---|---|
committer | Prefetch | 2021-12-01 19:38:28 +0100 |
commit | 63966407338ed0bdb061ddfd67f8940c2ccb51d2 (patch) | |
tree | f1d69af7e57b546c4f70fde2655d434bbb4bd323 | |
parent | c7d44d4d1c74152e49d4a21f41635aa21c5f6333 (diff) |
Expand knowledge base
-rw-r--r-- | content/know/concept/random-phase-approximation/dyson.png | bin | 0 -> 9803 bytes | |||
-rw-r--r-- | content/know/concept/random-phase-approximation/index.pdc | 185 | ||||
-rw-r--r-- | content/know/concept/random-phase-approximation/pairbubble.png | bin | 0 -> 12614 bytes | |||
-rw-r--r-- | content/know/concept/random-phase-approximation/rpasigma.png | bin | 0 -> 28365 bytes | |||
-rw-r--r-- | content/know/concept/random-phase-approximation/screened.png | bin | 0 -> 18085 bytes | |||
-rw-r--r-- | content/know/concept/self-energy/dyson.png | bin | 14164 -> 14904 bytes | |||
-rw-r--r-- | content/know/concept/self-energy/fullgf.png | bin | 16504 -> 16781 bytes | |||
-rw-r--r-- | content/know/concept/self-energy/index.pdc | 9 | ||||
-rw-r--r-- | content/know/concept/self-energy/selfenergy.png | bin | 36654 -> 27003 bytes | |||
-rw-r--r-- | sources/know/concept/random-phase-approximation/main.tex | 221 | ||||
-rw-r--r-- | sources/know/concept/self-energy/main.tex | 18 |
11 files changed, 419 insertions, 14 deletions
diff --git a/content/know/concept/random-phase-approximation/dyson.png b/content/know/concept/random-phase-approximation/dyson.png Binary files differnew file mode 100644 index 0000000..e92dbf8 --- /dev/null +++ b/content/know/concept/random-phase-approximation/dyson.png diff --git a/content/know/concept/random-phase-approximation/index.pdc b/content/know/concept/random-phase-approximation/index.pdc new file mode 100644 index 0000000..970a884 --- /dev/null +++ b/content/know/concept/random-phase-approximation/index.pdc @@ -0,0 +1,185 @@ +--- +title: "Random phase approximation" +firstLetter: "R" +publishDate: 2021-12-01 +categories: +- Physics +- Quantum mechanics + +date: 2021-11-15T21:01:34+01:00 +draft: false +markup: pandoc +--- + +# Random phase approximation + +Recall that the [self-energy](/know/concept/self-energy/) $\Sigma$ +is defined as a sum of [Feynman diagrams](/know/concept/feynman-diagram/), +which each have an order $n$ equal to the number of interaction lines. +We consider the self-energy in the context of [jellium](/know/concept/jellium/), +so the interaction lines $W$ represent Coulomb repulsion, +and we use [imaginary time](/know/concept/imaginary-time/). + +Let us non-dimensionalize the Feynman diagrams in the self-energy, +by measuring momenta in units of $\hbar k_F$, +and energies in $\epsilon_F = \hbar^2 k_F^2 / (2 m)$. +Each internal variable then gives a factor $k_F^5$, +where $k_F^3$ comes from the 3D momentum integral, +and $k_F^2$ from the energy $1 / \beta$: + +$$\begin{aligned} + \frac{1}{(2 \pi)^3} \int_{-\infty}^\infty \frac{1}{\hbar \beta} \sum_{n = -\infty}^\infty \cdots \:\dd{\vb{k}} + \:\:\sim\:\: + k_F^5 +\end{aligned}$$ + +Meanwhile, every line gives a factor $1 / k_F^2$. +The [Matsubara Green's function](/know/concept/matsubara-greens-function/) $G^0$ +for a system with continuous translational symmetry +is found from [equation-of-motion theory](/know/concept/equation-of-motion-theory/): + +$$\begin{aligned} + W(\vb{k}) = \frac{e^2}{\varepsilon_0 |\vb{k}|^2} + \:\:\sim\:\: + \frac{1}{k_F^2} + \qquad \qquad + G_s^0(\vb{k}, i \omega_n^F) + = \frac{1}{i \hbar \omega_n^F - \varepsilon_\vb{k}} + \:\:\sim\:\: + \frac{1}{k_F^2} +\end{aligned}$$ + +An $n$th-order diagram in $\Sigma$ contains $n$ interaction lines, +$2n\!-\!1$ fermion lines, and $n$ integrals, +so in total it evolves as $1 / k_F^{n-2}$. +In jellium, we know that the electron density is proportional to $k_F^3$, +so for high densities we can rest assured that higher-order terms in $\Sigma$ +converge to zero faster than lower-order terms. + +However, at a given order $n$, not all diagrams are equally important. +In a given diagram, due to momentum conservation, +some interaction lines carry the same momentum variable. +Because $W(\vb{k}) \propto 1 / |\vb{k}|^2$, +small $\vb{k}$ make a large contribution, +and the more interaction lines depend on the same $\vb{k}$, +the larger the contribution becomes. + +In other words, each diagram is dominated by contributions +from the momentum carried by the largest number of interactions. +At order $n$, there is one diagram +where all $n$ interactions carry the same momentum, +and this one dominates all others at this order. + +The **random phase approximation** consists of removing most diagrams +from the defintion of the full self-energy $\Sigma$, +leaving only the single most divergent one at each order $n$, +i.e. the ones where all $n$ interaction lines +carry the same momentum and energy: + +<a href="rpasigma.png"> +<img src="rpasigma.png" style="width:91%;display:block;margin:auto;"> +</a> + +Where we have defined the **screened interaction** $W^\mathrm{RPA}$, +denoted by a double wavy line: + +<a href="screened.png"> +<img src="screened.png" style="width:95%;display:block;margin:auto;"> +</a> + +Rearranging the above sequence of diagrams quickly leads to the following +[Dyson equation](/know/concept/dyson-equation/): + +<a href="dyson.png"> +<img src="dyson.png" style="width:55%;display:block;margin:auto;"> +</a> + +In Fourier space, this equation's linear shape +means it is algebraic, so we can write it out: + +$$\begin{aligned} + \boxed{ + W^\mathrm{RPA} + = W + W \Pi_0 W^\mathrm{RPA} + } +\end{aligned}$$ + +Where we have defined the **pair-bubble** $\Pi_0$ as follows, +with an internal wavevector $\vb{q}$, fermionic frequency $i \omega_m^F$, and spin $s$. +Abbreviating $\tilde{\vb{k}} \equiv (\vb{k}, i \omega_n^B)$ +and $\tilde{\vb{q}} \equiv (\vb{q}, i \omega_n^F)$: + +<a href="pairbubble.png"> +<img src="pairbubble.png" style="width:45%;display:block;margin:auto;"> +</a> + +We isolate the Dyson equation for $W^\mathrm{RPA}$, +which reveals its physical interpretation as a *screened* interaction: +the "raw" interaction $W \!=\! e^2 / (\varepsilon_0 |\vb{k}|^2)$ +is weakened by a term containing $\Pi_0$: + +$$\begin{aligned} + W^\mathrm{RPA}(\vb{k}, i \omega_n^B) + = \frac{W(\vb{k})}{1 - W(\vb{k}) \: \Pi_0(\vb{k}, i \omega_n^B)} + = \frac{e^2}{\varepsilon_0 |\vb{k}|^2 - e^2 \Pi_0(\vb{k}, i \omega_n^B)} +\end{aligned}$$ + +Let us evaluate the pair-bubble $\Pi_0$ more concretely. +The Feynman diagram translates to: + +$$\begin{aligned} + -\hbar \Pi_0(\vb{k}, i \omega_n^B) + &= - \sum_{s} \frac{1}{(2 \pi)^3} \int \frac{1}{\hbar \beta} \sum_{m = -\infty}^\infty + \hbar G_s(\vb{k} \!+\! \vb{q}, i \omega_n^B \!+\! i \omega_m^F) \: \hbar G_s(\vb{q}, i \omega_m^F) \dd{\vb{q}} + \\ + &= - \frac{2 \hbar}{(2 \pi)^3} \int \frac{1}{\beta} \sum_{m = -\infty}^\infty + \frac{1}{i \hbar \omega_n^B + i \hbar \omega_m^F - \varepsilon_{\vb{k}+\vb{q}}} \: \frac{1}{i \hbar \omega_m^F - \varepsilon_{\vb{q}}} \dd{\vb{q}} +\end{aligned}$$ + +Here we recognize a [Matsubara sum](/know/concept/matsubara-sum/), +and rewrite accordingly. +Note that the residues of $n_F$ are $1 / (\hbar \beta)$ +when it is a function of frequency, +and $1 / \beta$ when it is a function of energy, so: + +$$\begin{aligned} + \Pi_0(\vb{k}, i \omega_n^B) + &= \frac{2}{(2 \pi)^3} \int + \frac{n_F(\varepsilon_{\vb{k}+\vb{q}} - i \hbar \omega_n^B)}{(\varepsilon_{\vb{k}+\vb{q}} - i \hbar \omega_n^B) - \varepsilon_{\vb{q}}} + + \frac{n_F(\varepsilon_{\vb{q}})}{i \hbar \omega_n^B + (\varepsilon_{\vb{q}}) - \varepsilon_{\vb{k}+\vb{q}}} \dd{\vb{q}} + \\ + &= \frac{2}{(2 \pi)^3} \int \frac{n_F(\varepsilon_{\vb{q}}) - n_F(\varepsilon_{\vb{k}+\vb{q}})} + {i \hbar \omega_n^B + \varepsilon_{\vb{q}} - \varepsilon_{\vb{k}+\vb{q}}} \dd{\vb{q}} +\end{aligned}$$ + +Where we have used that $n_F(\varepsilon \!+\! i \hbar \omega_n^B) = n_F(\varepsilon)$. +Analogously to extracting the retarded Green's function $G^R(\omega)$ +from the Matsubara Green's function $G^0(i \omega_n^F)$, +we replace $i \omega_n^F \to \omega \!+\! i \eta$, +where $\eta \to 0^+$ is a positive infinitesimal, +yielding the retarded pair-bubble $\Pi_0^R$: + +$$\begin{aligned} + \boxed{ + \Pi_0^R(\vb{k}, \omega) + = \frac{2}{(2 \pi)^3} \int \frac{n_F(\varepsilon_{\vb{q}}) - n_F(\varepsilon_{\vb{k}+\vb{q}})} + {\hbar (\omega + i \eta) + \varepsilon_{\vb{q}} - \varepsilon_{\vb{k}+\vb{q}}} \dd{\vb{q}} + } +\end{aligned}$$ + +This is as far as we can go before making simplifying assumptions. +Therefore, we leave it at: + +$$\begin{aligned} + \boxed{ + W^\mathrm{RPA}(\vb{k}, \omega) + = \frac{e^2}{\varepsilon_0 |\vb{k}|^2 - e^2 \Pi_0(\vb{k}, \omega)} + } +\end{aligned}$$ + + + +## References +1. H. Bruus, K. Flensberg, + *Many-body quantum theory in condensed matter physics*, + 2016, Oxford. diff --git a/content/know/concept/random-phase-approximation/pairbubble.png b/content/know/concept/random-phase-approximation/pairbubble.png Binary files differnew file mode 100644 index 0000000..c082d19 --- /dev/null +++ b/content/know/concept/random-phase-approximation/pairbubble.png diff --git a/content/know/concept/random-phase-approximation/rpasigma.png b/content/know/concept/random-phase-approximation/rpasigma.png Binary files differnew file mode 100644 index 0000000..87ba3cc --- /dev/null +++ b/content/know/concept/random-phase-approximation/rpasigma.png diff --git a/content/know/concept/random-phase-approximation/screened.png b/content/know/concept/random-phase-approximation/screened.png Binary files differnew file mode 100644 index 0000000..e8b56e1 --- /dev/null +++ b/content/know/concept/random-phase-approximation/screened.png diff --git a/content/know/concept/self-energy/dyson.png b/content/know/concept/self-energy/dyson.png Binary files differindex efa7a63..f576632 100644 --- a/content/know/concept/self-energy/dyson.png +++ b/content/know/concept/self-energy/dyson.png diff --git a/content/know/concept/self-energy/fullgf.png b/content/know/concept/self-energy/fullgf.png Binary files differindex 3c88c6a..5767dba 100644 --- a/content/know/concept/self-energy/fullgf.png +++ b/content/know/concept/self-energy/fullgf.png diff --git a/content/know/concept/self-energy/index.pdc b/content/know/concept/self-energy/index.pdc index c86f8c5..7e67143 100644 --- a/content/know/concept/self-energy/index.pdc +++ b/content/know/concept/self-energy/index.pdc @@ -172,7 +172,7 @@ $$\begin{aligned} &= \frac{\displaystyle\sum_{n = 0}^\infty \frac{1}{2^n n!} \bigg[ \sum_{m = 0}^{n} \frac{n!}{m! (n \!-\! m)!} \binom{1 \; \mathrm{external}}{\mathrm{order} \; m}_{\!\Sigma\mathrm{all}} \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; (n \!-\! m)}_{\!\Sigma\mathrm{all}} \bigg]} - {\displaystyle\sum_{n = 0}^\infty \frac{1}{2^n n!} \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; n}_{\!\Sigma\mathrm{all}}} + {-\hbar \displaystyle\sum_{n = 0}^\infty \frac{1}{2^n n!} \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; n}_{\!\Sigma\mathrm{all}}} \end{aligned}$$ Where the total order is the sum of the orders of all considered diagrams, @@ -186,8 +186,7 @@ $$\begin{aligned} &= \frac{\displaystyle\sum_{m = 0}^{\infty} \frac{1}{2^m m!} \binom{1 \; \mathrm{external}}{\mathrm{order} \; m}_{\!\Sigma\mathrm{all}} \bigg[ \sum_{n = 0}^\infty \frac{1}{2^{n-m} (n \!-\! m)!} \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; (n \!-\! m)}_{\!\Sigma\mathrm{all}} \bigg]} - {\displaystyle\sum_{n = 0}^\infty \frac{1}{2^n n!} - \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; n}_{\!\Sigma\mathrm{all}}} + {-\hbar \displaystyle\sum_{n = 0}^\infty \frac{1}{2^n n!} \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; n}_{\!\Sigma\mathrm{all}}} \end{aligned}$$ Since both $n$ and $m$ start at zero, @@ -195,7 +194,7 @@ and the sums include all possible diagrams, we see that the second sum in the numerator does not actually depend on $m$: $$\begin{aligned} - G_{ba} + -\hbar G_{ba} &= \frac{\displaystyle\sum_{m = 0}^{\infty} \frac{1}{2^m m!} \binom{1 \; \mathrm{external}}{\mathrm{order} \; m}_{\!\Sigma\mathrm{all}} \bigg[ \sum_{n = 0}^\infty \frac{1}{2^n n!} \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; n}_{\!\Sigma\mathrm{all}} \bigg]} {\displaystyle\sum_{n = 0}^\infty \frac{1}{2^n n!} \binom{\mathrm{0\;or\;more\;internal}}{\mathrm{total\;order} \; n}_{\!\Sigma\mathrm{all}}} @@ -245,7 +244,7 @@ you can convince youself that $G(b,a)$ obeys a [Dyson equation](/know/concept/dyson-equation/) involving $\Sigma(y, x)$: <a href="dyson.png"> -<img src="dyson.png" style="width:90%;display:block;margin:auto;"> +<img src="dyson.png" style="width:95%;display:block;margin:auto;"> </a> This makes sense: in the "normal" Dyson equation diff --git a/content/know/concept/self-energy/selfenergy.png b/content/know/concept/self-energy/selfenergy.png Binary files differindex 8eaffff..55e182e 100644 --- a/content/know/concept/self-energy/selfenergy.png +++ b/content/know/concept/self-energy/selfenergy.png diff --git a/sources/know/concept/random-phase-approximation/main.tex b/sources/know/concept/random-phase-approximation/main.tex new file mode 100644 index 0000000..11c9bde --- /dev/null +++ b/sources/know/concept/random-phase-approximation/main.tex @@ -0,0 +1,221 @@ +\documentclass[11pt]{article} +\usepackage[utf8]{inputenc} +\usepackage{amsmath} +\usepackage{amsfonts} +\usepackage{physics} + +\usepackage{feynmp} +\DeclareGraphicsRule{*}{mps}{*}{} + +\begin{document} + +\begin{center} + {\Huge \sc Feynman diagrams} +\end{center} + +\noindent +Definition of RPA self-energy +\begin{align*} +\frac{\Sigma_s^\mathrm{RPA}(\vb{k}, i \omega_n^F)}{-\hbar} +&\equiv \:\: +\begin{fmffile}{sigma1order} + \begin{fmfgraph*}(30,20) + \fmfipair{i,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- o} + \fmfi{fermion}{i{up} .. tension 2 .. {down}o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: + \:\: +\begin{fmffile}{sigma2order} + \begin{fmfgraph*}(55,20) + \fmfipair{i,a,b,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{a}{(0.33w,0h)} + \fmfiequ{b}{(0.67w,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- a} + \fmfi{fermion}{a{up} .. tension 1.5 .. {down}b} + \fmfi{fermion}{b{down} .. tension 1.5 .. {up}a} + \fmfi{boson}{b -- o} + \fmfi{fermion}{i{up} .. tension 2 .. {down}o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{a} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{b} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: + \:\: +\begin{fmffile}{sigma3order} + \begin{fmfgraph*}(90,20) + \fmfipair{i,a,b,c,d,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{a}{(0.2w,0h)} + \fmfiequ{b}{(0.4w,0h)} + \fmfiequ{c}{(0.6w,0h)} + \fmfiequ{d}{(0.8w,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- a} + \fmfi{fermion}{a{up} .. tension 1.5 .. {down}b} + \fmfi{fermion}{b{down} .. tension 1.5 .. {up}a} + \fmfi{boson}{b -- c} + \fmfi{fermion}{c{up} .. tension 1.5 .. {down}d} + \fmfi{fermion}{d{down} .. tension 1.5 .. {up}c} + \fmfi{boson}{d -- o} + \fmfi{fermion}{i{up} .. tension 3 .. {down}o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{a} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{b} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{c} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{d} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: + \: \cdots +\\ +&= \:\: +\begin{fmffile}{sigmashort} + \begin{fmfgraph*}(40,20) + \fmfipair{i,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{dbl_wiggly}{i -- o} + \fmfi{fermion}{i{up} .. tension 2 .. {down}o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\end{align*} +Definition of screened interaction +\begin{align*} +\frac{W^\mathrm{RPA}(\vb{k}, i \omega_n^B)}{-\hbar} += \:\: +\begin{fmffile}{intshort} + \begin{fmfgraph*}(25,20) + \fmfipair{i,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{dbl_wiggly}{i -- o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: &\equiv \:\: +\begin{fmffile}{int1order} + \begin{fmfgraph*}(20,20) + \fmfipair{i,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: + \:\: +\begin{fmffile}{int2order} + \begin{fmfgraph*}(48,20) + \fmfipair{i,a,b,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{a}{(0.33w,0h)} + \fmfiequ{b}{(0.67w,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- a} + \fmfi{fermion}{a{up} .. tension 1.5 .. {down}b} + \fmfi{fermion}{b{down} .. tension 1.5 .. {up}a} + \fmfi{boson}{b -- o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{a} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{b} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: + \:\: +\begin{fmffile}{int3order} + \begin{fmfgraph*}(80,20) + \fmfipair{i,a,b,c,d,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{a}{(0.2w,0h)} + \fmfiequ{b}{(0.4w,0h)} + \fmfiequ{c}{(0.6w,0h)} + \fmfiequ{d}{(0.8w,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- a} + \fmfi{fermion}{a{up} .. tension 1.5 .. {down}b} + \fmfi{fermion}{b{down} .. tension 1.5 .. {up}a} + \fmfi{boson}{b -- c} + \fmfi{fermion}{c{up} .. tension 1.5 .. {down}d} + \fmfi{fermion}{d{down} .. tension 1.5 .. {up}c} + \fmfi{boson}{d -- o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{a} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{b} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{c} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{d} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: + \: \cdots +\end{align*} +Dyson equation for screened interaction: +\begin{align*} +\begin{fmffile}{dysonlhs} + \begin{fmfgraph*}(30,20) + \fmfipair{i,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{dbl_wiggly}{i -- o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: &= \:\: +\begin{fmffile}{dyson1rhs} + \begin{fmfgraph*}(30,20) + \fmfipair{i,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\:\: + \:\: +\begin{fmffile}{dyson2rhs} + \begin{fmfgraph*}(80,20) + \fmfipair{i,a,b,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{a}{(0.33w,0h)} + \fmfiequ{b}{(0.67w,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{boson}{i -- a} + \fmfi{fermion}{a{up} .. tension 1.5 .. {down}b} + \fmfi{fermion}{b{down} .. tension 1.5 .. {up}a} + \fmfi{dbl_wiggly}{b -- o} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{i} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{a} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{b} + \fmfiv{decor.shape=circle,decor.size=4,label.angle=-90,label.dist=3}{o} + \end{fmfgraph*} +\end{fmffile} +\end{align*} +Pair bubble definition: +\begin{align*} +-\hbar \Pi_0(\vb{k}, i \omega_n^B) +&= \qquad\:\: +\begin{fmffile}{pairbubble} + \begin{fmfgraph*}(30,20) + \fmfipair{i,o} + \fmfiequ{i}{(0,0h)} + \fmfiequ{o}{(w,0h)} + \fmfi{fermion,label=$\tilde{\vb{k}}\!+\!\tilde{\vb{q}}$,label.dist=3}{i{up} .. tension 1.5 .. {down}o} + \fmfi{fermion,label=$\tilde{\vb{q}}$,label.dist=3}{o{down} .. tension 1.5 .. {up}i} + \fmfiv{decor.shape=circle,decor.size=4,label=$\tilde{\mathbf{k}}\!\leadsto$,label.angle=160,label.dist=5}{i} + \fmfiv{decor.shape=circle,decor.size=4,label=$\leadsto\!\tilde{\mathbf{k}}$,label.angle=20,label.dist=5}{o} + \end{fmfgraph*} +\end{fmffile} +\end{align*} + +\end{document} diff --git a/sources/know/concept/self-energy/main.tex b/sources/know/concept/self-energy/main.tex index 114b433..e359053 100644 --- a/sources/know/concept/self-energy/main.tex +++ b/sources/know/concept/self-energy/main.tex @@ -15,8 +15,8 @@ \noindent Full Green's function -\begin{align} - G(b,a) +\begin{align*} +-\hbar G(b,a) &= \quad \begin{fmffile}{0order1} \begin{fmfgraph*}(30,20) @@ -67,10 +67,10 @@ Full Green's function \end{fmfgraph*} \end{fmffile} \quad + \:\: \cdots -\end{align} +\end{align*} Self-energy definition -\begin{align} -\Sigma(y,x) +\begin{align*} +\frac{\Sigma(y,x)}{-\hbar} =\!\!\!\! \begin{fmffile}{selfenergy} \begin{fmfgraph*}(20,20) @@ -123,10 +123,10 @@ Self-energy definition \end{fmfgraph*} \end{fmffile} \:\:\: + \: \cdots -\end{align} +\end{align*} Dyson equation -\begin{align} -G(b,a) +\begin{align*} +-\hbar G(b,a) = \quad \begin{fmffile}{fullgf} \begin{fmfgraph*}(50,20) @@ -166,6 +166,6 @@ G(b,a) \fmfblob{15}{v} \end{fmfgraph*} \end{fmffile} -\end{align} +\end{align*} \end{document} |